Why do UK government ministers not vote on backbench motions?

Question

According to the BBC:

It is convention that ministers abstain when voting takes place on a backbench MP's motion

What is the history and reasoning behind this convention? Is it therefore impossible for a backbench MP to effect any political change?

Answer 1

I think you're asking two questions, however in response to the backbencher one...

The role of a backbencher is to provide key information about their constituencies whilst they occupy an apprentice type role within government and are seen to be 'learning the ropes'.

If you look at the Wikipedia entry:

The term dates from 1855. A backbencher may be a new parliamentary member yet to receive high office, a senior figure dropped from government or someone who for whatever reason is not chosen to sit either in the ministry or the opposition Shadow Ministry. By extension, a backbencher is not a reliable supporter of all of their party's goals and policies.

So historically it may be related to wanting to avoid unreliable members that could act against the designated direction of the party. They are seen as vital in informing decisions but not so much in taking them as they may hold an opposing view to that of the majority of party members. Historically it was probably a way of protecting the best(or vested) interests of the rest of the party members from representatives that were perhaps not yet indoctrinated in the importance of certain policies. Though this is only what I imagine. Roles such as the chief whip could act to corroborate this view.

There is a good article one this website about the role of a backbencher and the powers that are allowed to them. Although this refers to the Australian system there is little difference that I see.

Abridged extract:

Backbenchers obviously have less impact on law-making than a minister – yet there are a number of ways they can influence both the content of legislation and the legislative process:

By serving on a parliamentary committee. This is perhaps where MPs on the backbenches can have the most impact. Committees engage in detailed scrutiny of existing legislation, hear from experts, consider public submissions and ultimately make recommendations about suggested changes to legislation. Some backbenchers with no leadership role in the parliament or their party can take a lead role in these committees, particularly on issues of great concern to them.

By participating in debate about bills. After the commencement of the Second Reading, a date will be allocated for parliamentary debate about a proposed bill. MPs can attend and speak for or against the bill or its specific parts. Their speeches are recorded in Hansard, which may be consulted by judges if the bill becomes legislation.

By suggesting amendments to a bill. During consideration in detail, MPs who object to specific parts of a bill – but not to the bill as a whole – may suggest amendments. Each amendment has to be voted on by the house but, if accepted, it will become part of the bill.

By raising a private member’s bill. Not all bills begin with the Cabinet or ministers. Any MP can introduce a bill into the parliament, with or without the support of the government. Because of this, private member’s bills are often voted down after the Second Reading and rarely move beyond their house of origin. Only 15 private member’s bills have been passed by the Federal parliament since 1901. The most recent of these was the Euthanasia Laws Act (2007), introduced by Liberal MP Kevin Andrews to overturn pro-euthanasia legislation passed by the Northern Territory. The Federal government allowed a conscience vote on the issue, rather than organising MPs to vote along party lines.

By raising suggested law reforms in the party room. This is where all MPs in a political party meet regularly to discuss matters pertaining to parliament and policy. Individual MPs can float ideas and lobby for changes to the law within their own party. These proposals may or may not be accepted and acted upon by ministers and the Cabinet.

From this we can see that they can affect change within parliament however less than frontbenchers.

Hope this helps!

Answer 2

It's not the case that ministers abstain on backbench motions. A recent example is a debate on a bill tabled by Conservative backbench MP Peter Bone called the "Wind Farm Subsidies (Abolition) Bill". This bill is an example of a private members' bill. The second reading of that bill took place on 6 March and can be read online at http://www.theyworkforyou.com/debates/?id=2015-03-06b.1216.0

In a second reading debate, the MP who is the sponsor of the debate moves the motion "that the Bill be now read a Second time" and gives a speech for why the bill should become law. As can be seen from the transcript, there was a speech against the bill from Julie Elliott MP, the Labour shadow minister. It was followed by a speech from the minister (also a Conservative), Matthew Hancock MP. His speech mentioned that the government opposed the bill.

At the very end, the question is put and if MPs disagree then there is a division (a vote). In this example there was a vote and the question was "negatived". A number of ministers voted against including the minister who spoke, Matthew Hancock.