Former chancellor Rishi Sunak is leading the race to become the UK's next prime minister as Conservative MPs declare who they are supporting

Although Sunak hasn't officially said he is running, it's believed he will do so soon and he already has the backing of more than 100 Tory MPs

That's the threshold needed to get on the ballot, with nominations closing at 14:00 on Monday

Boris Johnson has travelled back to London from a Caribbean holiday as speculation grows that he will also run

Sources planning his possible campaign say he too has the required number of backers, but Sunak's supporters call for proof

Trade minister Sir James Duddridge said the former prime minister told him that he was "up" for making a bid to return as PM

Commons leader Penny Mordaunt is the only candidate officially in the race, but she is lagging behind on Tory MPs' public support

Rishi SunakandBoris Johnsonremain the two frontrunners in the race, but neither the former chancellor nor the former prime minister have officially confirmed they are running

The BBC understands that the pair were due to meet this afternoon, but the meeting was pushed back for reasons that are unclear

Johnson's supporters have claimed the former PM has the support of 100 Tory MPs

But Sunak's backers have cast doubt on those claims, demanding Johnson's camp to publish a list of MPs who are backing him

Penny Mordauntcontinues to be the only official candidate to declare she's running for the top leadership position

Those wishing to throw their names in the hat have untilMonday at 14:00 BSTto find100 backers. The general public doesn't have a say on who will become the next Tory leader, but Conservative Party members will (unless MPs unite around just one candidate)

Currently203 out of 357 Tory MPshave gone public with their support.

Some127 MPsare backingSunak,53 MPssaid they'll supportJohnsonand a further23 MPshave pledged their support toMordaunt. (BBC)