MEP Robert Kilroy-Silk has stepped up his campaign to be leader of the UK Independence Party.
Kilroy-Silk is campaigning for the top job
Mr Kilroy-Silk has written to UKIP's 300 local branch chairmen calling for an "open, honest and grown-up debate" about the party's future.
He is attempting to oust Roger Knapman as the party's leader.
In the letter, the ex-chat show host asks "do we want a party with vision, with a clear sense of purpose" or "one that remains on the political fringe?"
'Chat show party'
The letter attacks Mr Knapman, a former Conservative MP, and Nigel Farage, UKIP's group leader in the European Parliament, as a "self-selecting cabal" who wanted to make "dishonourable pacts" with Eurosceptic Tory MPs.
Mr Kilroy Silk has urged UKIP activists to "kill" the Tory party and called for the party to field candidates in every constituency at the next general election.
UKIP's leadership have said the party would not stand against Eurosceptic Tories.
Mr Kilroy-Silk and Mr Knapman failed to settle their differences at a meeting of the party's 12 MEPs last week in Brussels.
Mr Kilroy-Silk claims Mr Knapman had agreed to stand down after UKIP's strong showing in the European elections in July.
But Mr Knapman denies any deal was struck and insists he intends to serve the remaining two years of his tenure as leader.
Earlier this month, Mr Knapman said Mr Kilroy-Silk had to become a "team player".
"Nobody is bigger than the party. We are a political party and not a chat show party," he told BBC News Online.
Mr Kilroy-Silk is to push ahead with his campaign to fight every Parliamentary seat by speaking at a meeting in Wokingham, the constituency of eurosceptic Tory John Redwood, on Wednesday.