The richest-ever man in Britain is not Lakshmi Mittal, the NRI steel tycoon, but Alan Rufus, an immigrant from northern France, ‘The Richest of the Rich’ list indicated on Sunday.

At present day value, his fortune is estimated to be worth more than 81 billion pounds - three times the wealth of Bill Gates, the co-founder of Microsoft. But Rufus, or Alan the Red, can never spend it. He died more than 900 years ago.

He heads a list of 250 people in a new book, ‘The Richest of the Rich’, by Philip Beresford, compiler of The Sunday Times ‘Rich List’ and Bill Rubinstein, a professor of history at Aberystwyth University.

Their study stretches back to the Norman conquest of 1066 and includes medieval barons, moneylenders and monks, as well as modern-day billionaires. Mittal, who topped the ‘Rich List’ three years in a row with a fortune now worth 19.25 billion pounds, just scrapes into the top 20 at No 20, while Roman Abramovich, owner of Chelsea Football Club, is at No 59 with 10.8 billion pounds.

When he died at the age of 53 in 1093, Rufus had a fortune of 11,000 pounds.

Beresford and Rubinstein, using figures from probate records and ancient documents, calculate that the sum represented more than 7 per cent of the net national income of the time. With an equivalent percentage today, Rufus would be worth 81.33 billion pounds, making him easily the richest Briton of all time.

Rufus was accused of abducting Gunhilda, daughter of King Harold, from a convent and seducing her. But he left no children and his estates passed to his brothers. His legacy is Richmond Castle, above the River Swale in North Yorkshire.

His uncle, William the Conqueror,  granted him vast tracts of land as reward for joining his army — 250,000 acres in Yorkshire, Norfolk, Suffolk, Cambridgeshire, Northamptonshire and London.