Conservative MP Mark Harper has become the 12th candidate to join the race to replace Prime Minister Theresa May.
The former chief whip told the Daily Telegraphhe was “quite happy to acknowledge that in this contest I am the underdog”.
He faces 11 other candidates, including five current and four former cabinet ministers.
The winner, expected to be announced by the end of July, will succeed Mrs May as Tory leader and UK prime minister.
Mr Harper, MP for the Forest of Dean, was a minister in the Home Office and Department for Work and Pensions during the 2010-2015 coalition government and is a former chief whip.
Who will replace Theresa May?
The winner of the contest to lead the Conservative Party will become the next prime minister.
He resigned as an immigration minister in 2014 after it emerged that his cleaner did not have permission to work in the UK.
“We’ve seen basically the same faces saying the same things that they’ve been saying for the last three years,” he told the Daily Telegraph.
“A number of them have tried to position themselves as fresh faces but I’m afraid they’ve sat around the cabinet table sharing the responsibility with the prime minister.”
The other declared candidates are:
• Brexit minister James Cleverly
• Environment Secretary Michael Gove
• Health Secretary Matt Hancock
• Foreign Secretary Jeremy Hunt
• Home Secretary Sajid Javid
• Former Foreign Secretary Boris Johnson
• Former Leader of the House of Commons Andrea Leadsom
• Housing minister Kit Malthouse
• Former Work and Pensions Secretary Esther McVey
• Former Brexit Secretary Dominic Raab
• International Development Secretary Rory Stewart
Former Conservative leader Iain Duncan Smith said the rules should be changed so candidates needed more MPs to back them.
Speaking on Thursday, Mr Duncan Smith told the BBC the threshold needed for MPs’ nominations should be “much higher” and the contest should be speeded up in its early stages.
“I have never seen so many people lining up and there may be more,” he said.
“We need to present a face of a party that actually can get jobs done,” he said. “We don’t want to have this meandering around looking like chaos.”
But Charles Walker, co-chairman of the Conservative 1922 Committee which sets the rules, played down the prospect of any change.
He told the BBC: “This is a leadership contest. We’re not going to artificially limit the number of candidates who can stand.”