David Campbell-Bannerman, the party's deputy leader, has said that only 15 per cent of funds donated to Ukip through a call centre in Kent has been paid into the party's head office accounts.

Outrage over the Ashford call centre has been blamed for the resignations of at least six senior party officials over the past 18 months.

Five former members of the party's national executive committee, Ukip's governing body, have told this newspaper they believe about £500,000 is unaccounted for in the party's head office accounts.

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