Boris Johnson stunned MPs by branding his government's hated "rape clause" an "injustice" which needs rectifying.
The Prime Minister shocked onlookers in the Commons with his remarks given the Government has staunchly defended its policy, which is connected to 2017 reforms to limit tax credits to a family's first two children.
A clause in the rules means women who have a third child as a result of rape can be exempted - but would have to provide evidence to do so, a move fiercely criticised by campaigners.
After his comments at Prime Minister's Questions, SNP MP Alison Thewliss, a long-time anti rape clause campaigner, said Johnson might have blundered.
On social media, she wrote: "My guess is he doesn't know what he's talking about. The two-child limit and the rape clause stigmatise, impoverish and must be scrapped."
Labour leader Jeremy Corbyn raised the tax policy at PMQs. He said: "The Prime Minister supports the absolutely horrendous rape clause in the child tax credit rules.
"Why does he think it's right that 200 mothers have to prove to the Government their child was conceived as a result of being raped so they can keep their child tax credits?"
Johnson, in his reply, said: "On his point about the recipients of benefit, he draws attention to an injustice and we will do everything we can to rectify it."
Corbyn responded: "I hope that means the Prime Minister is going to introduce regulations to end the two-child policy in the benefits strategy because that is exactly what happens when women who are victims of rape have to prove they've been raped in order to get benefits for their child."
Ministers have repeatedly faced calls to abandon the policy of limiting tax credits to a family's first two children.
