Video report by ITV News Political Correspondent Libby Wiener
Some Tory leadership hopefuls "are clearly positioning themselves for a Cabinet job" and so it is time to review how the race is run in the future, a member of the powerful 1922 Committee has revealed.
As former chief whip Mark Harper threw his hat into the ring, swelling the field to 12 as he did so, Nigel Evans, an executive member of the 1922 told ITV News it was in danger of getting out of hand.
He said that with days still to go before declarations close, the field could reach up to 20 - and some candidates were or would be "clearly positioning themselves for a Cabinet job", rather than hoping to be the next leader, and that was wrong.
Mr Evans revealed the Committee is due to meet next Tuesday and a review of how many publicly-declared backers potential candidates would need before standing was high on the agenda.
ITV News Political Correspondent Libby Wiener provides an analysis of the review
The Ribble Valley MP continued that if someone is putting themselves forward as leader of the party - and ultimately prime minister - then they should be able to display a degree of public support before entering the ballot.
"I think it is important that we have only credible people going forward, otherwise we will end up with 20-odd people, some of whom have absolutely no chance at all but what they do really want is a Cabinet job...
"Well, I've got a good idea, just support the person who you think is going to give you that and ideally support somebody who you believe in their principles," he said.
At the moment, candidates need only a proposer and seconder to stand.
He said there should not be a repeat of the 2016 leadership race where Andrea Leadsom pulled out at the last minute, leaving Theresa May to sweep to victory.
The last two this time around, said Mr Evans, must go to the membership, take part in debates and pitch their credentials.
He expected that once the first ballot is conducted on June 13, then the field would soon be whittled down.
The 1922 Committee meets weekly to discuss concerns of Tory backbenchers of how the leadership of the party is performing and carries considerable weight in feeding back opinion on frontbench policies.
Former Tory leader Iain Duncan-Smith echoed the concerns raised about the size of the field, likening it to a "Charge of the Light Brigade".
He urged the Committee to look at the rules around who could run and how much support they actually had - even though, he suspected, a number of hopefuls would swiftly realise they had no chance of getting into Number 10.
Meanwhile, Hereford and South Herefordshire MP Jesse Norman said he was "consulting" on whether to enter the race or not, but acknowledged if he did so, he would be a "minnow up against whales".
He said he was taking soundings from the public and fellow MPs and it would soon become clear where he stood.
Mr Evans said he was "serious" about amending the rules surrounding leadership contests - although it will not affect this race.
The official deadline for nominations is the week beginning June 10 - so there is still plenty of time for others to declare.
There will be a series of votes by Tory MPs to whittle down the field before just two are left standing to put themselves before the party membership.
Mr Evans said he was confident a winner would be confirmed before the summer recess.