The Tories are extending the deadline for applications to become their London mayoral candidate by six months.
Nicholas Boles is among the candidates to have come forward
It comes after radio host Nick Ferrari, the most prominent name connected with the candidacy, pulled out this week.
Labour claimed the contest had become a "farce" as the Tories scrambled to "find someone people might recognise".
The Tories insisted some "very serious potential candidates" were poised to enter the race to challenge Ken Livingstone in 2008.
Party chairman Francis Maude said they had asked for more time to consider their applications.
The Conservatives are planning to give Londoners the final say over their candidate in a series of X-Factor-style public votes designed, in the words of leader David Cameron, to "fire the public's imagination".
But high-profile figures including Lord Coe and Michael Portillo are reported to have turned down the chance to take part.
Eight candidates were thought to have entered the race by the original Friday deadline.
The only nationally known figure to put his name forward so far is Nicholas Boles, an ally of Mr Cameron, who stood unsuccessfully in Hove at last year's general election.
Others include London Assembly member Richard Barnes, Kensington and Chelsea councillors Victoria Borwick and Warwick Lightfoot, Territorial Army Major James Cleverly and Andrew Boff, who was beaten by the party's candidate in 2004, Steve Norris.
Lee Rotherham, who is campaigning to abolish the mayoralty and Lurline Champagnie, another local councillor, are also reported to have thrown their hats into the ring.
Mr Maude said the response had been "extremely encouraging".
But he added: "We have also received expressions of interest from a number of very serious potential candidates for whom the timescale we originally set is too restrictive.
"Given that the mayoral elections are still nearly two years away, we are therefore extending the deadline to give these and others the chance to come forward.
"We want as wide a range of people as possible to take part in this exciting and innovative process with a view to selecting a candidate next spring."
Labour chairman Hazel Blears seized on the decision as evidence Mr Cameron's leadership was running out of steam, saying "instead of finding the next big thing, the Conservatives have reverted to the same old thing".
She added: "The Conservatives have paraded the usual line-up of failed Parliamentary candidates, old-fashioned Thatcherites and even a candidate who wants to abolish the mayor altogether.
"As a consequence of this latest Cameron failure the Tories have descended into farce by now deciding to move their own mayoral candidate deadline in an attempt to find someone people might recognise."
Liberal Democrat president Simon Hughes said Mr Cameron's attempts to modernise the Conservative Party were "failing one after another".
"Now the clever idea to hold a London mayoral primary election has bitten the dust.
"Reforming the Tory party is clearly proving more difficult than David Cameron imagined," said Mr Hughes.