Banks including HSBC and NatWest are closing and freezing accounts held by charities working in conflict zones over fears they are financing terrorism, researchers warned yesterday.

A lack of government guidance on how banks should respond to counter-terrorism legislation has resulted in overly risk-averse actions being taken towards such charities, according to the Overseas Development Institute.

One charity, which requested to remain anonymous in the ODI report, was forced to forgo donations worth £2 million in the last 12 months as a result of funds being blocked by a bank.

Salaries paid to the bank accounts of aid workers who live outside Britain have also been delayed or blocked by banks, it claimed.