Josef Szrajber, 71, and Paolo Sorelli, 54, sold sensitive information about tenders for engineering work, mainly to Japanese and German companies looking to win North Sea contracts.
Judge Valerie Pearlman said at Southwark Crown Court: 'You quite deliberately as a business pursued a course of conduct where you obtained the information about the contents of sealed tenders so you could sell this information to other companies competing for the award of very lucrative contracts.
'What each of you did was strike at the very root of commercial probity, and that has to be treated very seriously indeed.'
She added that until hearing of both men's special circumstances she would have jailed them for six years.
Judge Pearlman ordered Szrajber to pay compensation of pounds 407,000 and Sorelli pounds 429,000. Each man will serve a further five years in prison in default and will pay pounds 65,000 costs.
Szrajber, of Mayfair, London, came to Britain from Poland in 1938. As well as his London home he and his wife own a listed country mansion. Sorelli, of Bayswater, west London, owns a penthouse and an Italian estate.Reuse content