Home Secretary Theresa May and Former Mayor of London Boris Johnson are set to enter the race to become the next Tory Leader and Prime Minister.
They will declare their candidacies, setting out how much support they enjoy and how they propose to unify the party after the Brexit vote.
Ex-minister Liam Fox is also throwing his hat into the ring, joining Work and Pensions Secretary Stephen Crabb.
The outcome of the contest to succeed David Cameron is due on 9 September.
Cameron, who has been Tory Leader for 10 years and led the country since May 2010, is stepping down after losing the vote on the UK’s future membership of the EU.
He has said fresh leadership is required to take on the task of negotiating the UK’s separation from the EU.