Prince Charles paid £3.3m in tax in 2005-06 on an income of more than £14m, a figure up 6% from last year on the strength of commercial property rent reviews and higher investment returns.

The prince’s principal private secretary Sir Michael Peat said: “In the first full year since the marriage of Charles and Camilla, the duchess is very much to the fore in the report. I think the prince and the duchess are becoming a powerful force for projecting British interests.”

However, veteran socialist commentator Harry Marks said: “He would say that, wouldn’t he? How a couple of useless old toffs ‘project’ British interests beyond hosting pointless balls for the polo playing crowd is beyond me.

“He should have paid a lot more tax than that if he really wanted to help Britain.”