Image caption Prince William and Kate Middleton are getting married in Westminster Abbey on 29 April

The government is consulting Commonwealth countries about changing the laws on royal succession, Deputy Prime Minister Nick Clegg has said.

At present, the law of primogeniture means male heirs accede to the throne before any older sisters.

Mr Clegg, who is responsible for constitutional reform, told the BBC the issue would "require careful thought".

But he said both he and David Cameron were "sympathetic" to changing rules which seemed "a little old fashioned".

Speaking to the BBC, Mr Clegg said: "Prince William and Catherine Middleton might have a baby daughter for instance as their first child, I think most people in this day and age would think it's worth considering whether we change the rules so that that baby girl then could become the future monarch.

"I think that would be in keeping with the changes that happen in society as a whole."

But he said it was not a "straightforward" process because the decision would have to be approved by all Commonwealth countries.

"It's something that affects other countries - New Zealand, Canada, Australia and so on - and we're having consultations at official level with those governments," he said.

Analysis It is an ancient discriminatory law, which despite plenty of talk, has remained resolutely unchanged on the statue book. Nick Clegg is the latest politician to enter the "lion's den" that is the 1701 Act of Settlement. He acknowledges any reform won't be straightforward and won't take place overnight - not least because it would require fresh legislation in the 15 other countries where the Queen is head of state. And if you tinker with succession, you have to address what one Scottish cardinal has called "state sponsored sectarianism" - the three centuries old law which bans a monarch from being a Roman Catholic or marrying one. With sources close to Mr Clegg stressing this isn't a political priority, it's likely we'll still be discussing this issue when Kate Middleton gives birth to her first child - especially if it is a girl. Follow Peter Hunt on Twitter

"My own personal view is that in this day and age the idea that only a man should ascend to the throne I think would strike most people as a little old-fashioned.

"I think it is worth thinking about, I think it is worth talking about. It is worth looking at what other countries that would be affected also feel on the subject," he added.

A Buckingham Palace spokeswoman said it was a matter for the government and would not comment.

The most recent attempt to steer changes to the rules on succession through Parliament was by Labour former minister Keith Vaz in January.

At the time Downing Street said any attempt to change the law would be a "difficult and complex matter", with parallel legislation needed in all Commonwealth nations where the British monarch was head of state.

Mr Vaz said: "I welcome the announcement by Nick Clegg that the government is consulting on primogeniture in royal succession.

"I hope that they will give their full support to my bill which is currently before Parliament.

"If they do so we can resolve this matter before any child of Prince William and Kate Middleton is born, not afterwards. The clock is ticking. We need to act fast."

The 1701 Act of Settlement bars any Catholic or anyone married to a Catholic from ascending to the throne, while Common Law gives precedence to male heirs in the succession of the throne.