Douglas Carswell is not Ukip's first MP

Conservative MP Douglas Carswell has announced he is defecting to Ukip.

He is, however, not Ukip's first MP, despite what you might have read on Twitter.

That 'honour' goes to Bob Spink, who defected to Ukip in April 2008 after resigning the Conservative whip the month before.

To complicate things further, Spink was redesignated as an independent MP by November 2008; on the grounds Ukip had no whip in the Commons.

Spink has also distanced himself from claims he was a Ukip MP. Speaking in 2009 he insisted he was never a member of Ukip, despite being listed as a Ukip MP when speaking in the Commons up until November 24.

At the 2010 general election he unsuccessfully stood for re-election in Castle Point, Essex, as an independent candidate who backed Ukip.

Carswell's defection, which came at a surprise press conference in Westminster attended by Ukip leader Nigel Farage, included the announcement he was standing down as an MP and planned to fight the by-election triggered in his Clacton constituency, in Essex.

The prominent Eurosceptic said his position as a Tory MP had been made "untenable" and that he did not want to "muddle through" as a Ukip MP until next May's general election, explaining his decision to seek re-election - which he did not have to do.

"It's not enough that I leave the Conservative Party and join Ukip. I will now resign from parliament and stand for Ukip in the by-election that must follow,' he said.

The Conservative leadership are not serious about change. If I believed they were sincere about real change, I wouldn't be here.

• Douglas Carswell

Because of quirks in the UK's parliamentary system, MPs are technically forbidden from resigning, the procedure used involves appointing an MP to an "office of profit under the Crown", something usually undertaken by the chancellor.

While George Osborne won't exactly be rushing to do that, he also cannot technically be appointed to a Crown office while Parliament is in recess, as it currently is for the summer.

However, a House of Commons source told i100 that he could quite probably consider himself a Ukip MP from now on: "There is nothing that needs to be done procedurally in the House of Commons to confirm a change of party allegiance. It is a matter for the individual and the party’s concern."

So, to conclude:

Douglas Carswell has defected to Ukip, but:

• He (almost certainly) is not a paid-up member.
• Technically the Tory whip has not been withdrawn.
• He could still describe himself as a Ukip MP, up until he is allowed to resign.

Bob Spink was listed as a Ukip MP in the Commons in 2008, but:

• He was redesignated as independent.
• He later denied being a Ukip member.

Bob Spink was technically Ukip's first MP in the Commons, but if Douglas Carswell is re-elected by the voters of Clacton on a Ukip ticket after a by-election, he will become the party's first elected MP.

Clear?

More: Everything you need to know about Douglas Carswell in one tweet