Emily Thornberry, the shadow foreign secretary, has announced that she is entering the Labour leadership race and said she had warned Jeremy Corbyn that backing a general election would be an “act of catastrophic political folly”.

Attempting to move the debate on from Brexit, Ms Thornberry said that her party needed to choose a successor who was best placed to take on Boris Johnson.

She said: “When the Labour leadership contest begins – and I hope to be one of the candidates – the first question shouldn’t be about their position on Brexit, or where they live in our country.

“The first question should instead be: what’s your plan for taking on Boris Johnson over the next five years? And do you