According to the Sunday Time Rich List, which is due to be published tomorrow, the former deputy Prime Minister increased his wealth by £50 million in the past year.

His £250 million fortune makes him Northamptonshire's richest man, but only the 325th richest in the country.

The resident of Thenford in South Northamptonshire is chairman of the Haymarket Publishing group, which publishes a range of magazines including Autosport, football magazine Four Four Two and gadget magazine Stuff.

Discussing the company he said: "Haymarket is a very dynamic, expert and independent publishing company with a very wide range of high quality business and consumer titles.

"We see ourselves as a family business. We're 50 years old now and our interest is expanding the expertise we've built up in the UK into a global market."

Mr Hesletine also has a 1,200 acre farm near Banbury.

He has taken over the top spot as Northamptonshire's richest man from Tony Travis of Northampton-based builders merchants Travis Perkins.

He was ranked 225th in the 2007 rich list with a fortune of £340 million. But the latest list puts him at 428th in the country with an estate worth £198 million.

Other Northamptonshire residents included in the Rich List include Leon Max, the Russian millionaire who bought Lord Hesketh's family home of Easton Neston near Towcester for about £15 million in 2005.

He also fell down the Rich List to 525th place from 467th last year despite his £150 million fortune remaining the same.

The former owner of Weetabix, Sir Richard George was at the exact same level as Mr Max, also with a fortune of £150 million.

So far, only the top 20 residents in the East Midlands have been published so it is not yet known where Althorp resident Earl Spencer will appear in the table.

The Sunday Time has said it now takes a fortune of at least £80 million to make it into the top 1,000.