PADDY Ashdown has urged people in Witney to back ‘open Britain’ by rejecting the Conservatives in this month’s by-election.

The Liberal Democrat grandee said the October 20 poll was of national importance and a shock result could change the Government’s approach to Brexit.

Witney is a safe seat for the Tories, with David Cameron’s successor Robert Courts widely expected to secure a majority.

But Lord Ashdown claimed Prime Minister Theresa May would be watching the vote closely after her comments indicating the UK could completely leave the European Union’s single market drew fresh fire from businesses.

He also said Mr Courts’ decision to vote Leave in the EU referendum meant the Tory candidate was the wrong person to represent West Oxfordshire, which backed Remain by a margin of more than seven per cent.

The Lib Dem peer added: “This by-election comes at an extremely important time and could change government policy from closed Britain to open Britain.

"We can send a message.”

He likened the contest to the 1991 Ribble Valley by-election, when the Lancashire seat famously swung from the Tories to the Lib Dems in opposition against Margaret Thatcher’s poll tax – which was later abolished.

Lord Ashdown said: “Mrs May seems to have thrown her lot in with the Brexiteers, with those who want a closed Britain. I think she is wrong.

"And this by-election will affect the shape of British politics, it will be an important bellwether.”

His comments came as the Liberal Democrats continued to wheel out their big guns in the battle to woo Witney voters, with hundreds of volunteers mobilising to canvass the town.

The party’s leader, Tim Farron, has already visited the constituency three times during the campaign, with Lord Ashdown appearing yesterday and former Deputy Prime Minister Nick Clegg expected to visit today.

Lord Ashdown described Liz Leffman, the party’s candidate for Witney, as ‘formidable’, adding: “She is one of the best by-election candidates I have campaigned with, and I’ve done a lot of them.”

But responding to Lord Ashdown yesterday, Mr Courts insisted his vote in the EU referendum was “a personal decision” and had no bearing on his ability to represent Witney.

He added: “The country has now made the decision and Brexit means Brexit and this government led by Theresa May will make a success of it.

"If elected, I will be strong local voice in Parliament to ensure the deal we get is right for the people of Witney and West Oxfordshire.”