I am sorry that you have decided to defect from UKIP to the Conservative Party.
In your resignation email you said that your decision is a “principled decision”. Let me now call on you to exercise those principles to their logical conclusion.
You were selected as a candidate by UKIP, the voters who elected you voted UKIP. The people who supported your campaign, donated funds, delivered leaflets, and did all the hard work to get you elected did it for a UKIP candidate. The voters who put you in office were voting UKIP not Tory!
You should do the principled thing and resign your seat and allow the next UKIP candidate on the Party List to take up the seat. Not to do so is to betray the UKIP members and voters who put you where you are.
I think you are profoundly mistaken if you believe that David Cameron will actually deliver on his promises. The Tories have consistently betrayed our country on the EU issue since 1972. There is no reason to believe that will do anything differently going forwards.
You are also mistaken when you say that “UKIP has done its job in its campaign to bring about a referendum on Europe and introduce controls on immigration”. UKIP policy is to leave the European Union; failing there being a UKIP government to bring this about the next best thing is a free and fair referendum on membership.
The battle to bring that about is far from won. Cameron’s promises cannot be relied upon and the only way the next government can be brought to bring about a referendum is for there to be enough UKIP MPs to hold the balance of power.
As for your statement that the Tories can “offer strong immigration controls”, this is a laughable idea; Mr Cameron as already admitted that there is nothing that he can do about immigration from the EU because of the EU’s open borders policy, and immigration is not even going to figure in the Tory Manifesto.
You should do the decent thing and resign your seat! Just as our Tory defectors, Mr Carswell and Mr Reckless did recently.