Robin Cook has told MPs he was "proud to lobby" foreign countries on behalf of British interests.

During his weekly business statement to MPs the leader of the Commons said it was "absolutely right" that Tony Blair should lobby abroad on behalf of companies with British connections.

He hit back at Opposition attempts to continue the row over the letter sent by the prime minister to the Romanian government supporting Indian-born Labour donor Lakshmi Mittal.

Cook argued Mittal was resident in Britain, his headquarters were based in Britain and he employed 100 people in Britain.

He defended the prime minister's involvement saying it had been government practice for years.

"In four years as foreign secretary I lobbied for hundreds of British companies," Cook argued. "I never asked how many did they employ and make a threshold."

In one case he had lobbied on behalf of a Swedish company because British Aerospace made parts for the Grippen fighter aircraft.

The row had only come about because Labour had passed legislation to compel the publication of details of big party donations - something the Conservatives had failed to do.

"We have been transparent," he said.

He then questioned the role former Tory Party treasurer Lord Ashcroft who had been based in Belize for many years while making large contributions to Tory Central Office.

"I would be very interested to hear from any of the gentlemen opposite how many people he employed in Britain," he said.