Ukip has manipulated the selection of prospective parliamentary candidates and is run by Nigel Farage as an “undemocratic” cabal, according to claims in a leaked cache of documents seen by The Times.

More than a dozen activists previously loyal to the Eurosceptic party have resigned over perceived efforts by Mr Farage and his allies to remove long-serving Ukip members from standing as MPs and MEPs in winnable seats.

As Mr Farage attempts to broaden Ukip’s appeal and to capitalise on its recent successes, some of his most longstanding foot-soldiers have accused the party of ignoring its own rules on selection procedures to the benefit of favoured candidates.

Neil Hamilton, now Ukip’s deputy chairman, warned in a private email that its list of MEP candidates