Dr Usherwood said: "Following UKIP’s strong showing since the summer in opinion polls and in the Police & Crime Commissioner elections earlier this month, it is not so surprising that several within the Conservative party feel threatened by a rival that doesn’t seem to tie itself up in knots on the European issue.

"However, UKIP has yet to prove itself a real force in British politics, outside of European elections, so it is likely that Tory Central Office will choose to continue to manage UKIP by not giving it the legitimacy that a pact would imply. Voters largely don’t rate the EU as an important issue, so for now that looks like a reasonable assumption."