Plans to run electric trains between Bristol and London have been thrown in to doubt after the Tories refused to commit to the £1billion scheme.

The Conservatives are enjoying a double-point lead in opinion polls and are tipped to sweep to power next year with a majority of at least 70.

If that happens electrification of the Great Western line could be put on hold or ditched permanently.

Last week Transport Secretary Lord Adonis gave a "cast-iron" guarantee the major overhaul, which would shave 12 minutes off journey times between Bristol and London, would go ahead under a Labour government.

But in an interview during the Conservatives' annual party conference, Shadow Transport Secretary Theresa Villiers told the Evening Post that was a pledge she would not make.

"We recognise there are huge benefits that come with electrification," she said. "My concern about the government's announcement is they have not explained how they would pay for it.

"We all know the disastrous state of the government's balance sheet. They have finally started to acknowledge they are going to have to cut spending, yet Lord Adonis is writing blank cheques."

Ms Villiers, a Bristol university graduate, also threw doubt on Bristol International Airport's £150 million expansion plans.