A midsummer by-election in Henley is on the cards after two dates were revealed today for a vote to secure Boris Johnson's successor.

Conservative Party leader David Cameron will seek to capitalise on an anticipated win in today's Crewe and Nantwich by-election by calling an early poll in Henley, the Westminster seat due to be vacated by Mr Johnson, the new London Mayor.

Residents of Henley - a traditionally strong Tory seat - will probably go to the polls on June 26 or July 3.

Mr Johnson is effectively holding two offices at present - one at City Hall and one in Henley, where he has yet to quit.