Boris Johnson resignation LIVE: Race to become new Prime Minister starts to take shape

The race to succeed to Boris Johnson as Prime Minister could begin to take shape today as candidates start vying for position. Backbencher Tom Tugendhat has become the first contender to officially throw his hat into the ring amid reports the Conservatives plan to announce a new leader by September.

Following his resignation on Thursday lunchtime Mr Johnson said he would stay on in a 'caretaker' role until a new leader is found. But former Prime Minister John Major warned it would be 'unwise' for Johnson to remain in office until a permanent replacement is confirmed.

It comes after a chaotic 48 hours in which more than 50 MPs quit the Government. The revelation the PM knew about previous claims against deputy chief whip Chris Pincher, but promoted him anyway, then 'forgot' he’d been told, was the last straw for many Tories.

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Would-be contenders to claim the Tory crown are today assessing whether they have the support to mount leadership bids following the dramatic resignation of Boris Johnson. With no clear frontrunner, around a dozen potential candidates – including backbenchers as well as ministers – are thought to be weighing a challenge, PA's Whitehall editor Gavin Cordon writes.

Meanwhile there is growing pressure from senior Conservatives for Mr Johnson to immediately step down as Prime Minister and not wait for the election of a new leader. Following the tumultuous events in Westminster, some MPs fear a summer of 'chaos' if Mr Johnson remains in No 10 while the leadership contest – which could run for weeks or even months – plays out.

Former prime minister Sir John Major was among those backing calls for Deputy Prime Minister Dominic Raab to be installed as a