Downing Street has dismissed the latest cash for access row saying the prime minister was lobbying for British business.

Officials moved swiftly on Monday to try and damp down the row over revelations that he wrote a letter to the Romanian government supporting the sale of the country's nationalised steel firm, Sidex, to the Indian-born steel tycoon and billionaire Lakshmi Mittal, who gave Labour £125,000.

The prime minister was not aware that the company was owned by a Labour donor when he signed it and that it had taken "all of 30 seconds", the official spokesman said.