Labour frontbencher Emily Thornberry has apologised after posting a picture of herself speeding on a motorway at 81mph.

The Mail on Sunday said the shadow attorney general uploaded the photograph, taken by a backseat passenger, of her driving a Toyota Prius in the middle lane of the motorway.

Alongside it on her Instagram account she wrote “On my way to Labour Conference” – which was taking place in Liverpool – adding that she was “choosing a Labour Students disco playlist”.

She apologises unreservedly for this fleeting and totally unwitting moment

She apparently failed to spot that the car’s digital speedometer could be seen in the shot registering 81mph, when the legal limit on motorways is 70mph.

The image has apparently since been taken down.

Her spokesman said: “She is well aware that the speed limits are set where they are for a reason, and she apologises unreservedly for this fleeting and totally unwitting moment when she exceeded them on the drive to Liverpool.”