Britain's first transgender MP has pleaded guilty to the harassment of an ex-wife after sending her unwanted voice notes and messages.

Conservative politician Jamie Wallis, now known as Katie Wallis, admitted the 'harassment without violence' of Rebecca Wallis between February and March this year.

At Cardiff Magistrates' Court today, District Judge Rhys Williams accepted a basis of plea on the recommendation of top London barrister Narita Bahra KC.

Wallis pleaded guilty to sending four unwanted phone messages and one voice note, but allegations of driving by Rebecca Wallis's home were removed from the charge.

Wallis will next appear before the court on July 14 for sentencing.

Narita Bahra KC, appearing for the defence, said her client did not wish to put their former partner, or their children, through anything further.

'He has, on balance, taken the pragmatic view, and recognises that he has previously had a public profile and taken the view that he can be rearraigned,' she said.

Ms Bahra said a psychiatric assessment and a pre-sentence report would be needed ahead of sentencing.