A long-standing Barclays shareholder has blasted US activist investor Edward Bramson's plans to trim back the business's investment bank.

Bramson, who is chief executive of New York investment company Sherborne, last week confirmed that he is forcing the bank to hold a shareholder ballot at its annual meeting in May on his plan to become a non-executive director.

Fund manager Richard Buxton, who has invested more than 3 per cent of his Merian UK Alpha Fund in Barclays, : 'We have a holding in Sherborne, so Bramson does communicate with us and has come in to see us.

'But we don't agree with what he's trying to do. 

The idea that this is the right moment to significantly downsize the investment bank is wrong.

'We also think it's wrong [to think] that if you were to do so, you would magically release vast amounts of capital to shareholders.'

He also called for an overhaul of Barclays' culture to ensure all staff act with integrity in the wake of a scandal which saw boss Jes Staley fined £642,000 for wrongly trying to unmask a whistleblower. 

Barclays declined to comment.