Drugs giant GlaxoSmithKline is offering cash to help regenerate Boston Manor Park - as long as they can pave over part of it with 600 parking spaces.
Campaigners have been angered this week following the release of a council report which reveals that due to the recession and a 'squeeze on public funds' restorations to Boston Manor House and its grounds may only be possible by accepting GSK's offer.
Linda Massey, member of Friends of Boston Manor Park, fumed: "We have been kept in the dark about this report for so long now and we feel rather hurt as an active friends group not having access to this information.
"We knew there were going to be contentious issues, but this is very contentious.
"GSK staff already take up the park's car park, preventing visitors from using it, and now they want to use up the green space below the elevated section of the M4 to park more cars.
"Putting a car park there would hinder so many activities that we do."
The Forward Planning Report, due to be discussed next week, details plans for improvements to the rundown Grade I-listed house and park, as well as adjoining playing fields which are owned by the London Playing Fields Foundation.
As well as the need to restore and find a use for Boston Manor House, recommendations include the creation of new leisure and sporting facilities within the park and improving the facilities on the adjoining playing fields to create a 'combined sporting hub'.
In the report, council leader Peter Thompson congratulates GSK for being at the 'forefront of green travel' and supporting public transport by contributing significant funds.
But he added: "The company believes that all of the 'easy wins' have been taken in encouraging staff to switch travel modes and believe they need access to nearly 600 more car parking spaces if they are to occupy GSK House to its fullest potential."
Cllr Thompson admits GSK's parking proposals may be a necessary 'enabling' development to bring about the regeneration that may otherwise be unachievable because of funding limitations.
But Ms Massey, who is the group's fundraising co-ordinator, said: "We have improved that park no end. If they just talked to us about funding issues I'm sure we could help them think of other options."
Last week Lib Dem campaigners Andrew Dakers, Dinti Batstone and Mona Naqvi called for urgent action to be taken to save Boston Manor House, which is on English Heritage's National Register of Buildings at Risk.
The report will be discussed at Hounslow Council's executive meeting on February 24 at 7pm in Committee Room 1, Civic Centre, Lampton Road, Hounslow.