UK Independence party (Ukip) co-founder Nigel Farage will be contesting the safe Conservative seat of Bromley and Chislehurst, it has been confirmed.
The seat was made vacant following the death two weeks ago of Tory MP Eric Forth, 61, who had held the seat since 1997 and had a majority of 13,000 at the last general election.
Mr Farage is currently MEP for the south east, and his nomination is a sign of Ukip's optimism that it has a chance of picking up some of the support for Mr Forth, who was to the right of mainstream Conservative thinking.
It emerged yesterday that Mr Forth's wife, Carroll, was one of six people being considered to stand for the Tories for the London by-election.
David Cameron's controversial A-list of preferred candidates is not being used in the by-election, although a Tory spokesman said head office had been involved in the selection.
With just over 50 per cent women and ten per cent from ethnic minority communities, the list was dismissed by right wing Conservatives MPs last week as a collection of "pseuds and posers of London's chichi set".
The decision not to use it in the Bromley by-election is a diplomatic move - Mr Forth was deeply critical of many of Mr Cameron's attempts to modernise the Conservatives.
The other candidates being considered are Bob Neil, the leader of the Conservatives on the London Assembly and a close friend of the late MP; Michael Harries, the chairman of the local constituency association; Mary Macleod; Syed Kamall; and Colin Bloom.
Two independent candidates, John Hemming Clark and Chad Noble, have already announced their intention to challenge the Tories on a conservative ticket.
The Liberal Democrats have chosen local councillor Ben Abbotts to stand for their seat. In last year's election, Lib Dem candidate Peter Brookes got 20 per cent of the vote.
Labour has yet to announce its candidate - last year, Rachel Reeves won 22.2 per cent of the vote, coming in second place to the Conservatives.
Ukip won 3.2 per cent of the vote at the last general election, the same proportion as the Green party.