Boris Johnson could claim former Prime Minister allowance of up to £115,000 a year

The public duty cost was first introduced by Margaret Thatcher when she resigned in 1990 as a means of covering office and secretarial costs.

This allowance will be available to Mr Johnson and he is expected to claim the amount following his farewell speech on Tuesday morning. 

He will be replaced by Liz Truss, who was elected as the new leader of the Conservative Party yesterday.

Boris Johnson expected to claim PM allowance of over £100,000

Outgoing Prime Minister Boris Johnson makes a speech outside 10 Downing Street (Stefan Rousseau/PA) (Image: PA)

Administered by the Cabinet Office, the former PM would need to be supported by documentary evidence.

The funds can only be used for secretarial and office costs that have come from the top job rather than any private or parliamentary responsibilities.

Mr Johnson's spokesperson was asked whether he would receive the controversial public duty payment, he said: “I believe so. It certainly will be available to him.”

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However, it is unclear whether Mr Johnson will claim his ministerial severance pay of £18,860 which equates to three months of his prime ministerial salary of £75,440.

The former PM receives this amount in addition to his MP's salary of £84,144.

Liz Truss. Credit: PA (Image: PA)

Boris Johnson gives farewell speech as he stands down as PM

Boris Johnson gave his farewell speech as Prime Minister on Tuesday morning as he officially left his office.

Speaking of his own future, Mr Johnson compared himself to a “booster rocket” jetting off into distant lands as he resigned his post.

But he called for his party to support Liz Truss and unite behind her.

The outgoing Prime Minister added: “I say to my fellow Conservatives it is time for us all to get behind Liz Truss.

“It is time for us to deliver for the people of this country.

“I am proud to have discharged the promises I made to my party when you chose me.

“We are one whole and entire United Kingdom. Those that want to break it up can keep trying but they will never succeed.”

Mr Johnson will now formally tender his resignation to the Queen, alongside the new PM.

Buckingham Palace has confirmed that the Queen, 96, will receive both the incoming and outgoing leaders on Tuesday, September 6 at her private Highlands home in Balmoral for the first time.