An “outdated” law preventing Cabinet ministers from taking maternity leave will be replaced to enable the Attorney General to take time off after having a baby, Downing Street has said.

Suella Braverman announced in November that she is expecting her second child early this year. She is believed to be the most senior woman at Cabinet level to have a baby in office.

Under current rules, Mrs Braverman would have to resign if she wanted to take time off following the birth.

The Government will instead bring forward legislation – to be debated at all stages next week – to provide for six months’ paid leave.

Downing Street said the current laws offered female Cabinet ministers an unacceptable choice between either resigning from their position or not taking time off.

The Prime Minister’s official spokesman told a Westminster briefing: “The current rules are clearly outdated and need fixing, which is why we are introducing the Bill.

“At the moment women are offered the choice between either resigning from their position or taking time off to recover from childbirth, which is simply not acceptable in the modern times.”

Asked if the legislation would cover a future female prime minister, the spokesman said: “It would apply to anybody who holds a Government position, whether that’s a Cabinet minister, a junior minister or anybody who holds a Government position to allow them to take six months’ full paid maternity leave.”

It is understood that Mrs Braverman will be temporarily replaced as Attorney General until her leave is over.

Boris Johnson outlined the changes in a written statement.

He wrote: “Changes that I made to The Ministerial Code on becoming Prime Minister set out provision for junior ministers to be able to take maternity leave.

“However, this work-around relies on another minister taking on additional responsibilities and cannot be used for Secretary of State or individual offices, such as the Law Officers or the Lord Chancellor.

“Until now, the limits on the number of salaries that can be paid overall, and for individual offices has left the Government with limited flexibility to appoint cover should a Minister want to go on maternity leave.

“In the absence of that flexibility, a senior minister wishing to go on maternity leave would likely need to resign from the Government.

“The Bill creates a designation of ‘Minister on Leave’ which provides for ministers to take maternity leave. This will also apply to certain Opposition post holders too.

“Ministers on leave will remain part of the Government and be able to be briefed on matters and kept in touch with work, but will not be responsible for exercising the functions of the office from which they are on leave.”

Shadow Cabinet Office minister Rachel Reeves said the legislation was a “small but significant step forward for women’s rights in Parliament” – though criticised it for lacking provisions for paternity, adoption or shared parental leave.

She said: “The Attorney General will be the first Cabinet minister in UK history to take maternity leave with proper pay and cover.

“It is quite unbelievable that women Cabinet ministers throughout history have faced resignation or demotion when choosing to have children.

“Working women should not be forced to choose between having children and their career – whether that be a Cabinet minister or any other working mum.

“But this Bill is already out of date, with no provisions for paternity, adoption or shared parental leave.

“Labour intends to hold the Government to their word to work cross-party to introduce comprehensive legislation in the coming months to right this injustice.”