Many people who change their gender end up with "horrendous" results and are left feeling "badly damaged", Lord Robert Winston has warned.

The scientist and TV presenter warned that the implications of gender reassignment surgery are not properly understood, with many operations ending in complications and people's fertility left permanently damaged.

Speaking on the Today Programme on BBC Radio 4, he said that "results are horrendous in such a big proportion of cases".

He said 40 per cent of people who undergo vaginal reconstruction surgery experience complications as a result, and many need further surgery, and 23 per cent of people who have their breasts removed "feel uncomfortable with what they've done".

He added: "What I've been seeing in a fertility clinic are the long-term results of often very unhappy people who now feel quite badly damaged.

"One has to consider when you're doing any kind of medicine where you're trying to do good not harm, and looking at the long-term effects of what you might be doing, and for me that is really a very important warning sign."

He added that the long-term effects of taking hormones "are likely to affect reproductive function".

Professor Gary Butler, a leading expert in care for transgender children and teenagers, agreed that the effect on fertility was a "worry".