Richard, it is quite possible to belong to a party without agreeing to or supporting every policy which that party's leadership puts forward. All parties are in fact coalitions. Are you suggesting that parties do not change their policy in response to changes in the views of those in the party? You seem to suggest that Hannan and Helmer are being disingenuous when they say that they want to see the UK withdraw from the EU. Have you any direct evidence for that?
It is generally the case that where you see sweeping changes in the status quo, they come from outside the party system, not from within it. The parties are the guardians of the status quo. They are resistant to change, and reward obedience. Therefore, it is very unlikely that anyone within the party system will effect so fundamental a change as our withdrawal from the EU from within the party system.
However, it is very easy to be a "licensed dissident" within the system, and it is very much in the interest of the political parties to bring dissidents into the fold, not to accommodate them, but to neutralise them. Thus, whether Hannan and Helmer are genuine or not is irrelevant. The fact is that they act as the Judas goats, neutralising dissent and blocking change. Thus, their words are incompatible with their actions.