The NHS must "be prepared" for nearly two million Britons to question their gender in coming years, a health boss has said.

James Palmer, the medical director for specialised services at NHS England, said in the future he expected up to three per cent of the population would make contact with transgender health services at some point in their lives.

Speaking at a conference on Monday Mr Palmer said that the expansion and improvement of NHS services could cause the growth in demand to "accelerate".

"We've got to be prepared to start thinking about designing a healthcare service that will allow somewhere around one to three per cent of the population at some point in their lives having a discussion about their gender," he said.

Based on current population estimates, this would mean 1.97m people in the UK using gender identity services, with around 1.6m of these living in England.

He told the audience that "referrals to adult services have increased by 240 per cent over the last five year period.

"There are currently 7,500 adults waiting for an appointment with our services. No other specialist service has seen this growth, anywhere near. As a result there is absolutely not sufficient capacity in the system," he warned.