The firm is expected to receive up to pounds 20m from a Government quango to clean up the highly polluted area, even though this will increase the resale value of the land afterwards from zero to an estimated pounds 75m.
The chairman of the quango, English Partnerships, is Lord Walker, also a director of British Gas.
The privatised company is already getting ready to cash in once the millennium exhibition at the London site is over. Last month it secured planning permission for 3,000 homes, a business park and shops to be built on the land.
In total, from selling off the regenerated land after the exhibition, from the exhibition leases and the clean-up grant, the company is expected to benefit by about pounds 100m.
The choice of the site for the celebrations marking the year 2000 was announced last week by the Heritage Secretary, Virginia Bottomley. Greenwich beat Birmingham because it argued that it could provide an exciting exhibition based on the concept of time, as the site is on the Prime Meridian.
The land, however, is heavily polluted by a cocktail of cyanides, sulphur compounds and phenols - by-products of decades of town-gas production.
The plan to use Government money for the clean-up has had strong backing from Michael Heseltine, the Deputy Prime Minister, but it has infuriated environmentalists because it contravenes the principle of "let the polluter pay".
That Lord Walker, who as Energy Secretary in the 1980s privatised British Gas, is involved with both the quango and the company is likely to cause further controversy. Yesterday he denied involvement in the process of deciding to make an English Partnerships grant to British Gas. "It has been minuted at English Partnerships that if there were any decision concerning British Gas, because of my connections I could not be involved," he said.
The chief executive of English Partnerships, David Taylor, said his organisation became involved after he was asked by Mr Heseltine, who is a member of the Millennium Commission that selected Greenwich, to participate. The request was made before Greenwich's selection was known.
"Michael Heseltine asked us three weeks ago to see whether we could help. The millennium project is just one part of the gasworks site, but we are talking about cleaning up the whole thing. It will need big money, and for us big money is between pounds 15m and pounds 20m," he said. The decision on the grant has not yet been made.
Leading surveyors are in no doubt about the rise in value that will follow the clean-up. John Macdonald, valuation partner of the surveyors Fuller Peiser, said: "In recent years, nobody would touch the place with a barge pole. But with the decision to extend the Jubilee [Underground] Line to the site, the planning permission, the cleaning-up of the site, and the exhibition, it will be transformed.
"We are likely to see the land go from nothing to pounds 250,000 an acre. If they build houses right on the Thames waterfront it could be up to pounds 500,000 an acre."
A Friends of the Earth industrial and pollution campaigner, Roger Lilley, said: "Until now 'let the polluter pay' has been the theory. We will be very unhappy if Government money is used to pay for remedial work. British Gas should pay for their own clean-up."
British Gas, which made profits of pounds 986m before tax last year, says that it is acceptable for it to receive Government money towards the clean- up of the site because it has contributed pounds 20m towards the construction of the Jubilee Line extension to the Greenwich peninsula.
Under the terms of English Partnerships' grants, recipients are expected to pay some of the money back but not necessarily all of it.
The Labour Party has said it will raise the issue with Mrs Bottomley tomorrow. "The Government must strike a hard deal with British Gas about profits and capital values regarding this site," said Mark Fisher, a Labour National Heritage spokesman.
Your pounds 2bn that went astray
British Gas siphoned off up to pounds 2bn of its customers' cash over 10 years to pay for rebuilding its pipeline network - then transferred money to other arms of the business, leaving a debt of almost pounds 3bn. A 343-page draft report by accountants Arthur Andersen questions whether British Gas needed to collect pounds 200m a year from customers, saying pounds 30m would have been more reasonable. And it suggests that much of the cash has been swallowed by excessively high payments to unregulated company divisions Full report, page 2Reuse content