Former defence minister Liam Fox will tomorrow formally reveal plans to replace David Cameron as Conservative leader and Prime Minister.
David Cameron announced he would be stepping down on Friday, following the UK's vote to leave the EU.
And now Fox, who campaigned for a Leave vote, has told radio station LBC that he will seek to succeed Cameron.
Fox is only the second candidate to openly announce plans to run, following work and pensions secretary Stephen Crabb's launch this morning.
Johnson is favourite for the role, with bookies today offering 8/11 on him taking the reins from 9 September.
Nominations for the party's leadership are open until noon tomorrow.