Infuriated campaigners who have been fighting for more than a decade to save a historic mansion from demolition say they have been left in the dark over a legal battle to secure its future.

A bid to overturn rejected plans to demolish Athlone House and replace it with an eight-bedroom family home on the edge of Hampstead Heath was lodged with the Planning Inspecorate in July.

But the 5,500 protestors trying to protect Athlone House, in Highgate, were only told about the appeal by Camden Council last week following an administrative error.

The communication breakdown has led members of the Athlone House Working Group to claim they have been left with an “unreasonable” amount of time to make their objections officially known before a September 30 deadline.

Their call for the Planning Inspectorate to give them more time to make their voices heard has been backed by Hornsey and Wood Green MP Lynne Featherstone.

Michael Hammerson, vice-president of the Highgate Society, said: “This is the most controversial planning application in the area and yet they’ve managed to not tell anyone. This is going to put a really unfair burden on the local community.”

Campaigners should have had eight weeks to submit objections to the Planning Inspectorate but have been left with only three to make their submissions after the Planning Inspectorate and Camden Council failed to tell them that the appeal had been lodged in July.

The council has apologised to campaigners for the administrative error which prevented them telling campaigners sooner but the authority has supported their request for the Planning Inspectorate to give them until October 31 to object.

The society currently faces added pressure as it is also embroiled in another legal row over plans to develop much-loved land known as Highgate Bowl.

Plans to build three luxury homes on the site of the former Highgate Garden Centre, off Townsend Yard, were rejected by Haringey Council in December last year but developers are bidding to overturn the ruling.

The date of the planning appeal on September 30 falls on the same day as the deadline for objections to Athlone House, which Mr Hammerson says has placed the community under “impossible pressure” to fight both applications simultaneously.

“This causes us serious trouble,” he said. “Hopefully having our MP will make a difference, and we have no reason to believe the planning inspector will be unreasonable.”

A provisional date for the Athlone House appeal has been set for February 10.