The Prime Minister’s anti-corruption tsar has resigned as he claims it is “pretty clear” that Boris Johnson has broken Ministerial Code.

In a letter to Johnson, Conservative MP, John Penrose accused the Prime Minister of breaching the code as he failed to provide adequate leadership over partygate.

Penrose said: “The only fair conclusion to draw from the Sue Gray report is that you have breached a fundamental principle of the Ministerial Code – a clear resigning matter.

“But your letter to your independent adviser on the Ministerial Code ignores this absolutely central, non-negotiable issue completely. And, if it had addressed it, it is hard to see how it could have reached any other conclusion than that you had broken the code.”

He added: “As a result, I’m afraid it wouldn’t be honourable or right for me to remain as your anti-corruption champion after reaching this conclusion, nor for you to remain as Prime Minister either.

“I hope you will stand aside so we can look to the future and choose your successor.”

This comes as Johnson is set to face a no-confidence vote tonight following Sir Graham Brady, chairman of the 1922 Committee, saying: “The threshold of 15% of the parliamentary party seeking a vote of confidence in the leader of the Conservative Party has been exceeded.”

The secret ballot will take place between 6pm and 8pm on Monday, June 6.

If half of MPs vote that they do not hold confidence in Mr Johnson’s leadership, then he will be ousted.

But, as the rules currently stand, if Mr Johnson wins a confidence vote, he cannot be challenged again for 12 months.