Campaigners hoping to save a Victorian mansion from demolition have signed up a crack team of experts to fight their corner ahead of a last-ditch David and Goliath-style battle.

Community groups in Hampstead and Highgate are fighting against plans to demolish Athlone House on the edge of Hampstead Heath and replace it with a so-called “Arabian nightmare” eight-bedroom family home with basement car park and swimming pool.

Renowned experts, including an award-winning historian, have offered their services free of charge to protect the former RAF base and hospital in Highgate at a 12-day inquiry starting on Tuesday.

Despite their assistance, campaigners face a daunting battle against the derelict house’s mysterious owner, thought to be a foreign billionaire.

Highgate Society vice-president Michael Hammerson, who is leading the charge, said: “The developers will throw all the money in the world at it.

“Let’s just say, David had it easy against Goliath.”

It is estimated that developers Athlone House Limited have spent in the region of £1million on appealing against Camden’s decision last summer to refuse planning permission for the proposals.

It is the last chance for the owners to push proposals through.

Three experts have stepped in to spare local amenity groups the Highgate Society and Heath&Hampstead Society the same legal costs.

The societies had feared they would not be able to find the money to fund the costly fight after already plunging finances into a legal challenge over the Hampstead Heath dams project and an appeal against plans to build luxury homes on the Highgate Bowl.

Barrister David Altaras, a member of the Heath and Hampstead Society, will represent campaigners pro-bono at the public hearing.

The groups have also enlisted the help of expert witnesses, architectural historian Professor Joseph Rykwert CBE, who was awarded the Royal Institute of British Architects’ highest honour last year, and conservation engineer Jon Avent.

Highgate Society member Gail Waldman said: “We will be a voice for all those people who made their opinions very clear, that they love the house and that it is a house worth saving.”

Opponents of the plans want developers to stick to a historic obligation known as a section 106 agreement requiring the previous owners to restore the house.

A spokesman for Athlone House Limited said: “National planning policy has moved on since the previous appeal, and we are now confident that this house is eminently supportable.

“Although we are disappointed that the revised application was refused by Camden planning officers, a public inquiry will give all interested parties the opportunity to take part and make their views known to the planning inspector.”

The inquiry starts on Tuesday at 10am at the Wesley Hotel in Euston.