NEWLY elected Mayor of London Boris Johnson is to resign today as MP for Henley, triggering a by-election in the Oxfordshire constituency.Conservative leader David Cameron is expected to table a writ later today for the by-election to be held within weeks, with June 26 the date thought most likely for the poll.

Graham Dines

NEWLY elected Mayor of London Boris Johnson is to resign today as MP for Henley, triggering a by-election in the Oxfordshire constituency.

Conservative leader David Cameron is expected to table a writ later today for the by-election to be held within weeks, with June 26 the date thought most likely for the poll.

With a 12,793 margin of victory at the 2005 general election, Henley is one of the Conservatives' safest seats and defeat for Tory candidate John Howell would be a virtually unthinkable upset for Mr Cameron.

But Liberal Democrats are already campaigning hard in the seat, where they feel their candidate Stephen Kearney can make a dent on the Tory majority. Also standing are Richard McKenzie for Labour, Mark Stevenson for the Greens and Chris Adams for UKIP.

The by-election comes hot on the heels of Labour's shock defeat at Crewe and Nantwich on May 22. But the party has trailed in third place in Henley since 1970 and the by-election offers little opportunity for Gordon Brown to turn the electoral tide in his favour.