The shadow chancellor’s proposed Post Bank would have the biggest network of high-street banks

Labour’s shadow chancellor, John McDonnell, will today unveil plans to transform post offices into branches of a new nationalised bank.

A government led by Jeremy Corbyn would put £2.5bn into the “Post Bank” to save the high street and protect face-to-face banking. Britain has lost two-thirds of its bank and building society branches in the past 30 years.

The Post Office has a sprawling but struggling network of more than 11,500 branches. The state-owned business faces pressure from online delivery services such as Amazon and the wider decline of the high street but made a profit of £35m last year, up from £13m in 2016-17 — the first year that it had been in the black for 16 years.

Ministers have been criticised for letting