The UK Independence Party has lost one of its two London Assembly members to Robert Kilroy-Silk's new political party, expected to launch on Wednesday.
The party is still reeling from the departure of Robert Kilroy-Silk
Damian Hockney said ex-chatshow host Mr Kilroy-Silk would "deliver better" as the leader of a eurosceptic party.
He said Mr Kilroy-Silk had made him deputy party leader of Veritas, Latin for truth.
Sources close to Mr Hockney said around eight other members of London UKIP were also planning to jump ship.
Details of the coming week's events were hammered out at a meeting at Mr Kilroy-Silk's Buckinghamshire home on Sunday, the BBC News Website was told.
The news came after UKIP suspended a candidate for allegedly suggesting the criminally insane should be killed. John Houston, 54, was due to stand in the East Kilbride seat in Lanarkshire at the next election.
A spokesman for UKIP called on Mr Hockney to quit the London Assembly.
UKIP asserts that Mr Hockney "has a moral obligation, if not a legal one" to stand down.
Mr Hockney meanwhile told the BBC: "I believe that Robert Kilroy-Silk can deliver better as a leader of a eurosceptic party than the current leadership of the UK Independence Party."
On the suspension of Mr Houston, UKIP said those who selected him knew nothing of his views.
Mr Houston is alleged to have said that the organs of the criminally insane should be "made available to law-abiding members of the community" and proposed the legalisation of drugs and the sex trade.
The document reportedly said: "We're looking for the resurrection of the British Empire.
Mr Hockney says he is to be deputy leader of Veritas
"The problems for the human race - environmental and others - can only be dealt with on a global scale, and that calls for a radical alliance of the English-speaking nations, which they are uniquely able to do."
UKIP spokesman Mark Croucher said the main issue would be that Mr Houston's reported views had been presented as UKIP policy, which they were not.