A former Conservative chairman has switched her support in the EU referendum debate, complaining that moderate voices in the Brexit campaign have been drowned out by “lies and xenophobic campaigning”.

Dewsbury peer Baroness Warsi said her decision to change sides from Leave to Remain was sparked by an “indefensible” poster released by Ukip leader Nigel Farage, as well as “lies” from Michael Gove over the prospect of Turkey joining the EU.

But her defection was greeted with bemusement by the Leave campaign, with senior figures saying they were not aware that she had been a supporter.

The development came as MPs gathered in Westminster for a recall of Parliament to pay their respects to Labour MP Jo Cox , whose death in a violent attack on Thursday led to a three-day pause in the EU battle.

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Campaigning was expected to get back into full swing, with both sides making a final push for support in what appears to be a knife-edge vote.

Lady Warsi - who was the first Muslim woman to attend Cabinet but quit the Government in 2014 over the Gaza conflict, announced her defection in The Times, saying she could not support a campaign which included the Ukip “Breaking Point” poster depicting a column of migrants walking through the European countryside.

She later told the BBC Radio 4 Today programme: “This kind of nudge-nudge, wink-wink xenophobic racist campaign may be politically savvy or politically useful in the short term, but it causes long-term damage to communities.

“The vision that me and other Brexiters who have been involved right from the outset, who had a positive outward-looking vision of what a Brexit vote might mean, unfortunately those voices have now been stifled and what we see is the divisive campaign which has resulted in people like me and others who are deeply Eurosceptic and want to see a reformed relationship feel that they now have to leave Leave.”

Lady Warsi said she had argued for a “Hello World” approach to the Leave campaign, stressing “an optimistic vision of where Britain stands in the world, how it trades freely and is open to the brightest and best from around the world and is rooted in its humanitarian instinct”.