Alistair Darling yesterday defended the No campign’s acceptance of the donation from Vitol’s Ian Taylor

larceny in a deal with the Manhattan District Attorney in the US after paying what the firm called “surcharges” to Iraqi officials in Saddam Hussein’s regime under the United Nations oil- for- food scheme. The DA’s office described the payments as “kickbacks”.

In 2010, the US Commodity Futures Trading Commission (CFTC) fined two Vitol subsidiaries $6m for “wilfully failing to disclose material facts” to the New York Mercantile Exchange for almost two years. Vitol neither admitted nor denied the CFTC’s findings, but put in new compliance measures.

After a week’s silence, Darling yesterday defended Taylor – who has a key stake in the Harris Tweed industry. Darling said: “Ian has made clear his reasons for supporting Scotland as a strong part of the UK … we think that people should be able to speak out against the nationalists without facing this kind of personal attack.”

SNP Westminster leader Angus Robertson said the credibility of Darling and the No campaign was damaged by keeping the donation.

Better Together declined to comment on Vitol’s operations but said Taylor was a respected figure in Scotland and the UK.

AVitol spokeswoman said the firm was confident it was fully compliant with all relevant regulations globally, and that “all its tax affairs are compliant with the appropriate legislation in each of the jurisdictions in which it operates”.