BORIS Johnson has been urged by Cabinet minister Amber Rudd to publicly come out against "game-playing" in the Tory leadership race as talk of tactical voting mounts at Westminster.

Conservative MPs this morning voted to decide which two candidates will make the run-off before 160,000 party members.

Johnson supporter Jacob Rees-Mogg said any "dirty tricks" vote transfer campaign by supporters of the former Foreign Secretary to try and knock out rival Michael Gove of the contest would be "silly".

“People should always vote for the candidate they support,” declared the Chairman of the anti-EU ERG faction.

"It is really silly to try and game elections because you can find that your candidate then loses. Vote for the candidate you support is what I have been saying on my side of the argument," he added.

In 2016, Mr Gove's decision to stand for the leadership effectively torpedoed Mr Johnson's then campaign and the wounds have not healed.

Sources in the Johnson camp played down a strategy of the frontrunner lending votes to Jeremy Hunt to ensure the Scot is eliminated. Gove supporters have already warned against “heavy-duty shenanigans” by Johnson supporters.

Brexiteer backbencher Andrea Jenkyns, who is backing the former Foreign Secretary, suggested there would be "some poetic justice" if the two bitter rivals were in the final run-off.

Iain Duncan Smith, who is also supporting Mr Johnson, said: "I have been here long enough to know that the only dirty tricks is that MPs never tell you always the truth when it comes to leadership elections. They are unorganisable.”

Asked if there was a "dirty tricks" campaign against him, Mr Gove said: "I know there is a campaign for me with wonderful, wonderful people."

The Environment Secretary added: "I'm looking forward to being in the final two as a result of the strong support I have across the party."

Asked if he was confident after voting, Mr Hunt replied: "Confident but not over confident."

Asked if he knew anything about dark arts when he arrived to vote, Mr Johnson told reporters: "No."

The former London Mayor received a boost when the Evening Standard, edited by George Osborne, the former Chancellor, came out in support of him.

An editorial read: "Twice, the Evening Standard supported Boris Johnson to be the Mayor of London. Today we back him to be the next Prime Minister."

Earlier, addressing the issue of tactical voting Ms Rudd said: "I find all this conversation about lending votes rather discrediting of the system.

"I would really call on Boris himself to repudiate the information that is coming out of 'friends of Boris', saying this, saying one thing."

The Work and Pensions Secretary, who is backing the Foreign Secretary in the race for No 10, added: "This is a serious moment. We don't need that sort of game-playing going on in Parliament."

Referring to reports that Johnson supporters would vote strategically to try and scupper Mr Gove's chances of making the run-off, former Cabinet minister Nicky Morgan, who backs the Environment Secretary, told the BBC: "There has been all sorts of speculation.

"But, I would say to my colleagues, I think that is an extremely good reason why Michael absolutely should be in the final two."

Eliminated Tory leadership candidate Rory Stewart has said he will not publicly back any of the remaining contenders on Thursday.

He tweeted: "I will not be declaring for anyone today but I will be voting."

Mr Johnson appears certain to make it through to the next stage of the process, having topped the ballot in each of the three rounds of the contest so far and securing the votes of 143 of the 313 Tory MPs.

Mr Hunt, Mr Gove and Sajid Javid, the Home Secretary, also remain in the contest but two rounds of voting on Thursday - the first announced at 1pm - will whittle the field down to a final pairing.

At each round, the MP with the lowest total will be eliminated with the final announcement due to be made at 6pm.

The next Tory leader and prime minister will be chosen by Conservative members next month from the two candidates who make it through. A series of UKwide hustings will take place with the Scottish one, pencilled in for Perth, due on Friday July 5. The winner will be announced in the week beginning July 22.