Jackart, DK and the Nameless One are in a fight over the UKIP again. DK's response contains the same logical problem I've noted before. This sentence is a good example: "For fuck's sake, even the offer of an unloaded refendum would be good enough for me (and even for the majority of UKIP, I would imagine)." This assumes that the Conservative party's policy comes down from on high and that members should passively take or leave the opinions of the parliamentary party.
Parties are coalitions of people with broadly similar approaches to politics. The actual challenge for someone with a view outside the political mainstream (the position we share on climate change is another example) is, in the end, to find the party whose approach to politics is most compatible with their own and then try to convince them of the merits of their position. Once that party is convinced it can attempt to seek a parliamentary majority on that basis. If you do not like the leadership's position on the European Union then convince the membership and, at the next leadership election, you can get the kind of leaders you want.
As such, the only reason to leave the Conservative party is if you think its members aren't those who will be easiest to convince of your position (they're easily the most Eurosceptic portion of the population so that seems unlikely) or if you think your cause is hopeless but would rather be screaming at the wind than be dirtied by the compromise of contact with the Conservatives. If you can't convince the Conservative membership you're never going to be able to convince the public at large and the problem is in the case rather than the party.
Look at it this way: There are opportunity costs to the UKIP. Imagine if all the money, effort and people committed to the UKIP were, instead, within the Conservative party arguing and voting for change in its European policy. You wouldn't piss off loyal Tories by associating Euroscepticism with undermining right-wing electoral chances. What talent and funding UKIP possesses might be spent convincing people rather than on the paraphenalia of running a party. Eurosceptics wouldn't take the risk of strengthening the hand of the real europhiles in the Labour and Liberal Democrat parties.
Every time a Eurosceptic leaves the Tories and joins the UKIP they remove themselves from the debate within the Conservative party. They replace their voice and vote with a threat, to hurt Conservative election prospects, but there is no evidence that this is a threat which the party responds to in the way UKIP would like. Instead it creates a defensiveness that may be what came across to DK, in Oliver Letwin's speech, as arrogance. The best Conservative response electorally to the 'UKIP threat', so long as they are not convinced by its arguments, isn't to appease but to crush the smaller party. As such, the threat will continue to fail to have the effect you are looking for and the challenge remains to convince the Conservative party of the merits of leaving the EU.
I do not want to leave the EU but do have some positions on which the leadership does not represent my views; the proper response to climate change is one. On those issues I am doing all I can to change the minds of the public and fellow Conservatives. Setting up a new party would not be an effective means to that end.