With its £100,000 appeal already nearing its target, the Heath and Hampstead Society’s “Dam Nonsense” campaign against the City of London’s £15million pond proposals was given another boost this week.

The society’s solicitors sent a 14-page letter to the Corporation setting out its legal objections to the series of flood protection dams the City wants to build, which are due to be challenged in a judicial review later this year.

The “letter before action”, sent on Monday, which gives the City 14 days to reply, discloses the three major legal grounds for the challenge and calls on the City to rescind its original decision.

While its contents will be made public later, the three major legal grounds are:

* The decision is based on an erroneous interpretation of the words “in the interests of safety” in Section 10 of the Reservoirs Act 1975.

*  The decision is based on “an irrational and unlawful approach to risk.” 

* The decision is the result of a process that ought to have been subject to a strategic environmental assessment, which has not been carried out in accordance with European law.

“We have written to the City to invite it to rescind the decision and to take any further decisions regarding the ponds on the correct legal basis,” said Marc Hutchinson, newly-elected chairman of the society.

He revealed that the society has raised more than £80,000 towards the costs of a judicial review, now likely to be held in September or October.

“That campaign is by no means over,” said Mr Hutchinson, a leading City solicitor. “It is an interesting question as to why the appeal has been so successful so quickly. The answer is that the people who use the Heath and walk on it love it very much and are now quite concerned as to the impact on the landscape of these dam works.

“People have always felt this passion for their beloved Heath and have always funded campaigns to protect it. But we are in somewhat austere times and you can’t always presume you will be able to raise lots of money quickly from your members.”

He added: “We are advised that we have a well-arguable case and I am very hopeful of success. I am hopeful that the judge will see the strength of our argument and the fact that Hampstead Heath is a special if not unique case. That’s the essential point.”