It is worth noting that this may not be a pseudonym. In the UK you can legally change your name to virtually anything via deed poll as long as it doesn't fall under the following restrictions
- does not include at least one forename and one surname;
- is impossible to pronounce;
- includes numbers or symbols (see section 2 below);
- includes punctuation marks that do not have a phonetic significance. However, you can have a hyphen to link forenames or surnames (for
example, if you want a double-barrelled name) and an apostrophe in the
case of surnames like O'Brien;
- is vulgar, offensive or blasphemous;
- promotes criminal activities;
- promotes racial or religious hatred;
- promotes the use of controlled drugs or includes the generic or slang name for them;
- ridicules people, groups, government departments, companies or organisations;
- may result in others believing you have a conferred or inherited honour, title, rank or academic award, for example, a change of first
name to Sir, Lord, Laird, Lady, Prince, Princess, Viscount, Baron,
Baroness, General, Captain, Professor or Doctor etc.
- exceeds the maximum number of characters allowed in a name (see section 7 below).
As such with a deed poll document you can get the name on your passport also changed. Technically speaking therefore this may not be a pseudonym but his real legal name.
I can give you the example as cited in this article of another "personality" who stood in this election but in Westmorland and Lonsdale instead of Maidenhead, where one individual legally changed his name via deed poll to be called "Mr Fishfinger" to stand against the incumbent Tim Farron (Leader of the Liberal Democrats).
Indeed Britain has a long history of people changing their legal names to appear as a joke candidate on a ballot paper, a tactic often taken up by The Official Monster's Raving Loony Party.
Never mind the ballot box, there is a long list of appearances in newspapers where name changes have resulted in some funny situations, I can give this example from last year when Buzz Lightyear was fined £200 for speeding in Devon