Keir Starmer today said he has "concerns" over Scotland's gender recognition reforms, because he believes 16 is too young for someone to change their legal gender.
But he refused to say if he would overrule the new law if he was Prime Minister - as Rishi Sunak could decide to do this week.
The SNP government in Scotland passed legislation last month which will allow trans people to obtain a gender recognition certificate without the need for a medical diagnosis.
