The men who worked as agency staff  for several construction procurement advisers had access to confidential information that they offered for sale.

Disguised as “consultancy services”, the illicit payments from firms were shared out among the corrupt ring.

Contract information on £70m worth of work was traded on a series of high-value oil and gas engineering projects between 2001 and 2009 in Iran, Egypt, Russia, Singapore and Abu Dhabi.

Andrew Rybak, 55, from Newbury was jailed for five years, his co-conspirator Ronald Saunders, 65, from Hampshire was jailed for three and a half years.

The third man Philip Hammond, 57, from Belgium was also jailed for three years.

Another man from Hampshire, Barry Smith, 71, received a 12-month sentence, suspended for 18 months and 300 hours of unpaid work.

Rybak and Hammond were also disqualified from acting as company directors for 10 years.

Another suspect now lives in the Philippines and it has not been possible to bring him to trial in the UK.

The case, codenamed Operation Navigator, was launched after a Foster Wheeler office alerted police.

Foster Wheeler Worley Parsons, a joint venture in Reading, was awarded the Singapore Parallel Train procurement contract.

A man employed by the firm as a buyer passed information to Rybak and Hammond.

Rybak, using a false name, approached GE Water & Process Technologies offering information but the firm rejected the approach and reported it to the Foster Wheeler JV.

This led to City of London Police and the SFO being called in, and it became apparent to the investigators that several other projects were also tainted by corruption.

Passing sentence yesterday, HHJ Deborah Taylor, said: “All this was done without the slightest regard for the interests of others.

“Your activities in connection with these conspiracies had little, if anything, to do with the interests of those engaged with the project, but were parasitic, leeching money for your benefit.”

Contracts related to following projects ( defendants involved)

Styrene Monomer Project, Iran.  (Rybak, Saunders and Hammond)

QASR Gas Gathering Project, Egypt.  (Rybak and Saunders)

Sakhalin Island Project, Russian Federation. (Rybak, Saunders and Hammond)

Singapore Parallel Train Project.  (Rybak and Hammond)

Hydrogen Power Project, Abu Dhabi.  (Rybak, Saunders and Smith)