Nigel Farage will decide within hours if he will fight the by-election sparked by disgraced former Tory minister Patrick Mercer's decision to quit over a cash-for-questions scandal.
Mr Mercer admitted he was "ashamed" and had many regrets as he announced his intention to stand down as the MP for Newark after facing a six month ban from parliament.
The battle for the Nottinghamshire seat will come after next month's European Parliament elections in which Conservatives are expected to be forced into a humiliating third place and will be an unwelcome fight for David Cameron.
Although Mr Mercer secured a Conservative majority of 16,152 in 2010, the Prime Minister would come under intense pressure if Mr Farage capitalised on his party's popularity in the vote.
Mr Farage told the BBC: "I know that winning one seat in Westminster would completely transform the landscape for us as a party in terms of our prospects.
"What I've got to work out is, is it the right seat for me. And I just...my reservation in my mind is I haven't particularly got connections with the local area."
Mr Mercer said he believed he had to "fess up and get on with it" after a sleaze watchdog yesterday agreed plans to suspend him from the House of Commons.
The former army colonel is alleged to have tabled Commons questions and offered a Westminster security pass after signing a deal that paid him £4,000 for seeking the readmission of Fiji to the Commonwealth.
He told reporters in Westminster he was going to do what he could to "put it right" for the people of Newark and for his wife and family "who have been under such pressure for the last year".
Mr Mercer added : "As an ex-soldier I believe that when I have got something wrong you have got to fess up and get on with it.
"No point in shilly shallying and trying to avoid it. What's happened has happened and I'm ashamed of it."
Mr Mercer resigned the Tory whip when the allegations emerged in May last year to ''save my party embarrassment'' and said at the time that he would quit the Commons at the 2015 general election.
The decision by the Commons Standards Committee to impose a six month suspension from Parliament prompted him to bring forward the date.
Mr Mercer served as shadow homeland security minister until 2007, stepping down after suggesting that racism was ''part and parcel'' of life in the forces.
Labour sources said the party fights for every seat but pointed out that the Tories were 30 points ahead of them in 2010 and had double their vote in last year's council election .
Newark Conservative Association quashed speculation that Mayor of London Boris Johnson could stand in the seat by announcing that Robert Jenrick had been selected as the Tory candidate.
A Conservative spokesman said: "We agree that Patrick Mercer needs to stand down and that there should be a by-election so the people of Newark can have a new MP."