Lib Dems confident of taking Tory seats once held by Cameron and Johnson

Exclusive: Party sources say Tory support collapsing' in the south as they target additional 25 seats

The Liberal Democrats are increasingly confident they can beat the Conservatives in large parts of southern England, including the two Oxfordshire seats formerly held by David Cameron and Boris Johnson.

Ed Davey, the Lib Dem leader, spent Sunday campaigning in Bicester, where the party believes it can defeat the Conservative candidate, Rupert Harrison, a highly regarded economist and one-time adviser to the former chancellor George Osborne.