The concept of ethnicity has been described by the UK's highest court in this way
For a group to constitute an ethnic group... it must, in my opinion, regard itself, and be regarded by others, as a distinct community by virtue of certain characteristics. Some of these characteristics are essential; others are not essential but one or more of them will commonly be found... The conditions which appear to me to be essential are these: — (1) a long shared history, of which the group is conscious as distinguishing it from other groups, and the memory of which it keeps alive; (2) a cultural tradition of its own, including family and social customs and manners... In addition to those two essential characteristics the following characteristics are, in my opinion, relevant; (3) either a common geographical origin, or descent from a small number of common ancestors; (4) a common language, not necessarily peculiar to the group; (5) a common literature peculiar to the group; (6) a common religion... (7) being a minority or being an oppressed or a dominant group within a larger community, for example a conquered people (say, the inhabitants of England shortly after the Norman conquest) and their conquerors might both be ethnic groups.
A group defined by reference to enough of these characteristics would be capable of including... for example, persons who marry into the group... Provided a person who joins the group feels himself or herself to be a member of it, and is accepted by other members, then he is... a member...
In my opinion, it is possible for a person to fall into a particular racial group either by birth or by adherence, and it makes no difference... by which route he finds his way into the group...
...the word " ethnic " is of Greek origin, being derived from the Greek word " ethnos ", the basic meaning of which appears to have been simply " a group " not limited by reference to racial or any other distinguishing characteristics—see Liddell & Scott's Greek-English Lexicon (8th edition)
The official UK statistical body and the general structure of its surveys as they relate to ethnicity
In the United Kingdom the official body which gathers and publishes statistics is the Office for National Statistics.
Among other things it conducts a census every 10 years which everyone is required to complete. From 1991 census has asked questions about ethnicity.
The style of the ethnicity question used by ONS in the census is often also found in use by government departments and other public bodies (in the employment field) and is used by larger private companies.
The Ethnicity question is presented in the form of two large boxes (there is also a three, four and five large box versions but I will concentrate initially on the two large box version for simplicity of explanation - my question is pertinent whichever version is used).
The first large box contains a tickbox list containing e.g.
and ending with a Any other White background (please specify) box
Immediately to the right of that large box (or directly underneath it) is another large box which contains a tickbox list of ethnicities. These can vary to a degree over time but neither English, Scottish, Welsh nor Irish is ever in this list in the second large box. At the bottom of the list in the second large box there is a tickbox saying Any other non-White background (please specify)
The instructions say you can only choose one large box and only one box within that so that when statistics are presented in, for example, a pie chart (see here for example) the slices of the pie will be distinct and not overlap.
This means that the last option in each large box which says any other XXX background carries the meaning of any other XXX background not covered in any of the above rather than any other way you would like to describe your XXX background. A consequence of this is that the presence or absence of a particular predefined option can have a strong influence on the answer given. For example take the case of someone who considers themselves a Kerryman first and foremost, and only secondarily as Irish. If neither Kerryman nor Irish are in the predefined list in the large box they are completing they might tick Any other... and write Kerryman. But if Irish is in the predefined list and Kerryman is not they would tick Irish because although they identify with additional ethnicities it would not be true to say that their ethnicity is other than - i.e. not - Irish.
Some information about the United Kingdom for those not familiar with it
By way background for those not familiar with the United Kingdom, the UK is a unitary state which consists of the island of Great Britain and the north-east corner of the island of Ireland which is called Northern Ireland. Great Britain contains three countries England, Wales, and Scotland but, as you would expect, people who grew up in Wales, for example, or whose parents identify as Welsh, or for some other reason feel an affinity to Wales might describe themselves as Welsh even if they currently reside in England. Everyone who is Welsh, Scottish or English would describe themselves as British but people vary as to what they initially describe themselves as when asked - e.g. whether they immediately say British or immediately say e.g. Scottish. Most English people (and Welsh and Scottish people) have a light skin tone (which the ONS calls "white"). Historically (including before the emergence of English as a fully-fledged ethnicity with its own language) there have always been a minority of people on the island of Great Britain with noticeably darker skin tone (which the ONS calls "black") but because of intermarriage the number of people with distinctly darker than average skin remained relatively low until about 300 years ago when identifiable groups of people with dark skin emerged particularly in Liverpool and Cardiff and immigration in the last 100 years has increased that small minority to a large minority. Up until just over 200 years ago the whole of the island of Ireland was a single country - the Kingdom of Ireland. The Kingdom of Ireland and the Kingdom of Great Britain were then united as the United Kingdom of Great Britain and Ireland. About 100 years ago the majority of the land mass of Ireland became a separate state, the Republic of Ireland, but Northern Ireland remained part of the UK (now renamed the United Kingdom of Great Britain and Northern Ireland). Although some people in Northern Ireland might give Northern Irish (or "Ulster") as their ethnic identity, because the partition of the island of Ireland is relatively recent most people either identify as British or Irish. Of those who identify as Irish in Northern Ireland, the majority would actually prefer Northern Ireland to be part of the Republic of Ireland if that were to be possible and it is important for them to give their ethnicity as Irish and not Northern Irish - i.e. they do not want their expression of ethnicity to be artificially constrained to a subset of how they see themselves.
The experience of someone filling in the classic two large box survey form
If you consider an English person who is black filling in the Ethnicity question it is immediately apparent to them that the first large box is not for them. Usually the first large box will actually be headed White (and the second large box will be headed non-White) but even if the first large box is not headed White it is obvious from the last tickbox of the list
Any other White background (please specify)
that all the boxes above, including English are to be understood as only being appropriate for those who are white.
Turning to the second large box, English is not among the options listed (nor are Scottish, Welsh or Irish) but Caribbean is. At the bottom of the list it allows you to specify as an ethnicity
Any other non-White background (please specify)
but the words any other suggest that if any of the options listed above applies in any way that should be ticked and the any other option should not be ticked unless all the options listed above it are completely inapplicable. Most black people in the UK now are descendants of those who came to the UK from Caribbean islands within the last 70 years and may well consider themselves to have a Caribbean ethnicity as well as English, Scottish or Welsh etc. It is not necessary to prioritise ethnicities but even if they feel that English is their primary ethnicity they are likely to feel that they should tick Caribbean if that is one of their ethnicities and, having chosen that, they may feel that it does not seem right to choose any other instead (the instructions say tick one box only) even if they do not consider Caribbean to be their main ethnicity.
In any event writing English under any other non-White background does not seem right here because, whilst there are millions of English people who are black, English as a term is not itself a specifically non-White background
You would not want to put Black English because Black English is not an ethnicity. The whole idea of an ethnic group is that it is a group. Saying, in effect, you can't be part of our group but we will set up another group a bit like ours for people with skin like yours (as the ONS has actually done on more recent surveys with the Black British option) is not the same. This is similar to the position of a person with Irish ethnicity in Northern Ireland who objects to their expression of ethnicity being constrained to the subset Northern Irish.
This general proposition - that e.g. Black English is not a commonly recognised ethnicity - seems to be confirmed by ONS research into terms such as Black Welsh which concluded:
The combination of ethnic minority and UK identity, such as “Black Welsh”, was noticed in England, but was rarely noticed by ethnic minority respondents.
Some people (I imagine probably not from the UK) have given answers to this Politics SE question implying that the above ONS research shows that everyone in the UK thinks that you can only be of English (or Welsh) ethnicity if you are "white". This is a misunderstanding. It is precisely because Welsh and English ethnicity is not (and never has been) restricted to particular skin tones that Black Welsh is not recognised as a specific ethnicity - i.e. you can be black and ethnically Welsh but not Black Welsh as a specific ethnicity. Similarly you can be a blue-eyed Welshman but Blue Welsh is not an ethnicity.
The Ethnicity question in the 2021 Census form
The above describes the classic two large box system but more recently there seems to have developed a five large box version which can be seen in the paper version of the 2021 Census
Sometimes surveys are taken face to face and the ONS Guidance states:
What instruction should be used when asking the ethnic group question in a face-to-face interviewer-led survey and self-completion survey?
It is recommended that the ethnic group question will be asked in a way that allows the respondent to see all possible response options before making their decision. Therefore, in face-to-face interviewer-led surveys, a single show card should be used that presents all response options. The interviewer should then ask the respondent to select the option that best describes their ethnic group or background.
This makes clear that the fact that a black person inevitably sees, on the paper census form, a box headed White which includes within it the word English - thus suggesting that only white people can be English - is a deliberate design feature which it is important to show to all respondents before they state their ethnicity.
Completing the 2021 Census online
If you use the online version the gist of the first question is Are you White, Black, Asian or something else?
If you select White you are then given English as an option
But if you select Black (or Asian or any other high-level option other than White) you are taken to a screen which does not have English as an option. If you do this you will not have seen the screen which suggests that English is specific to the White group but you will be given a number of predefined options none of which is English.
So the survey form and online version provided by the ONS apparently does not cater for people who are not "white" who regard themselves as English. (The same applies to Scottish and Welsh.)
Note: the domicile question and it recent renaming
In order to ensure that nobody is missed off the census or double counted each household is required to fill it in based on who was present in the household on a ONS-specified date. Of course some people present in a household on a particular date may be staying there only temporarily so censuses have always asked about each person's domicile - i.e. where they usually live or where they call home. This question about domicile has, in the 2021 census been named "national identity" which may be liable to confuse because "identity" normally refers to something such as ethnicity rather than mere domicile but ONS notes make clear that this question is not about ethnicity. It is "not dependent on your ethnic group or citizenship". Of course not everyone reads the ONS notes and one might speculate as to why this question has been renamed so that it sounds a bit like ethnicity and has been placed immediately before the actual ethnicity question. What is clear is that if a black person enters English as an answer to this question it will have no effect on the recording of their ethnicity
The practice in other countries
I don't know about every other country but I know that France does not ask about ethnicity and most other EU member states do not either. The USA allows those answering to select any ethnicity or ethnicities in any combination - unlike with the UK ONS no combinations are ruled out or made difficult to select.
Prominent black Members of the UK Parliament have objected to people telling them that they cannot be English if they are black. In March 2021 David Lammy MP told a caller who said that he could not be English because he was black:
I want my identities recognised appropriately ... I’m of African descent, African-Caribbean descent but I am English.
So my question is
What is the rationale of preventing English people who are black (or indeed any English person with a skin tone darker than what the ONS regards as "white") saying on the census form (or in other surveys/questionnaires based on the same structure) that they are of English ethnicity?