New London mayor Boris Johnson said he would resign from his Henley seat
The Conservatives could capitalise on their first by-election victory in 26 years by setting a date to elect a new MP for Henley, in Oxfordshire.
The Tories took the Crewe and Nantwich seat in Cheshire on Thursday with a 17.6% swing from Labour.
The party may now set a mid-summer date for a Henley by-election after MP Boris Johnson said he would step down when he was elected mayor of London on 1 May.
Both 26 June or 3 July have been talked about as likely dates for a contest.
But Mr Johnson said any decision was in the hands of the local Conservative Association.
Mike Lewin, the deputy chairman of South Oxfordshire Conservatives, said: "I think we are still in the process of selecting a potential candidate to replace Boris.
"This will take a little while as we want to find the best candidate to win the seat and represent the people of Henley."
Labour's Richard McKenzie and the Liberal Democrats' Stephen Kearney have already been selected to fight a Henley by-election.
Mr Johnson succeeded former Deputy Prime Minister Michael Heseltine as MP for Henley at the 2001 general election with a majority of 8,458.
He was re-elected in 2005 with an improved majority of 12,793 and a 53% share of the vote.
Mr Johnson's father Stanley Johnson, a former MEP, has already coveted his son's seat.
"That would be the most tremendous honour, I cannot at this time think of anything I would more like to do," he said.