Boris Johnson furiously denies plotting against David Cameron after being caught asking about potential rebels

The former London mayor has denied asking Tory backbencher Alec Shelbrooke about the number of potential rebels within the party

Boris Johnson denied plotting against him saying he was just trying to make sure David Cameron had strong support after the referendum (Getty)

Boris Johnson has reportedly admitted to discussing the possibility of a leadership coup against David Cameron.

The former mayor visited Tory backbencher Alec Shelbrooke in his Westminster office and reportedly discussed how many potential rebels there were to trigger a no-confidence vote.

An anonymous source told the Mail on Sunday that Mr Johnson asked Mr Shelbrooke if there were the required 50 MPs to trigger a vote after the EU Referendum.

Mr Shelbrooke was overheard saying he thought Mr Johnson was “digging” for information and had told him there were only 20 rebels “at the most”.

The pro-Remain Elmet and Rothwell MP said Mr Johnson seemed “rattled” and “worried about how the next few months would pan out”.

But a friend of Mr Johnson have dismissed the report as “absolute b*******”.

Mr Johnson confirmed the conversation had taken place but said he and Mr Shelbrooke were discussing “how vital it was to keep the party together under Dave’s leadership”.

Under Conservative party rules 50 MPs have to write a letter to Graham Brady, the chairman of the influential 1922 Committee made up of backbenchers to call for the Prime Minister to step down.

The report comes Mr Cameron is under growing pressure as the EU referendum campaign has increasingly descends into “blue on blue” attacks.

Speaking on the Andrew Marr show on Sunday, Mr Cameron said despite the infighting he would not resign regardless of the vote on 23 June.

He said: “If we vote to leave will we carry out that instruction? Yes. Will I carry on as Prime Minister? Yes.

“Will I construct a Government that includes all the talents of the Conservative Party? Yes.”

Despite this many Tory MPs, particularly in the Leave camp, have called for his resignation.

Brexit supporter Nadine Dorries said she had “already sent her letter in” to Mr Brady when she appeared on ITV's Peston two weeks ago.

She said she was supporting Mr Johnson as the next party leader.

Mr Johnson is currently the second favourite to become leader when the next leadership contest happens according to a poll of party members by ConservativeHome - after Justice Secretary Michael Gove who has ruled himself out of the race.