Campaigners showed the strength of feeling behind a fight to save a beloved Victorian mansion on the edge of Hampstead Heath from demolition at the start of a planning inquiry today.

Concerned members of the public packed into a Euston hotel this morning to hear the case for and against demolishing Athlone House, off Hampstead Lane in Highgate.

Developers Athlone House Limited want to replace the former hospital and RAF intelligence base with an eight-bedroom family home with basement car park and swimming pool, referred to by campaigners as an “Arabian nightmare”.

Applause sounded as barrister David Altaras objected to the proposals on behalf of the Athlone House Working Group (AHWG) campaigners, made up of members of the Highgate Society, Heath&Hampstead Society and Highgate Conservation Area Advisory Committee (HCAAC).

He told the inquiry in an opening statement: “‘Ostentatious display of wealth, effusively decorated using brightly contrasting materials, designed to make a significant impression.’

“That is [architect] Professor Adams’ description of the original Athlone House, but it is a description that AHWG believes could and should be applied with much greater force to the present proposal.

“I am confident that everyone at this inquiry understands the fundamental aim of AHWG but for the avoidance of doubt I shall spell it out.

“We wish to retain this elegant mid-Victorian mansion.”

Barristers on behalf of Camden Council and the City of London Corporation, which manages Hampstead Heath, also made opening statements this morning to urge planning inspector Colin Ball to reject the appeal.

Barrister Robin Purchas QC, on behalf of Athlone House Limited, told the inquiry that the mysterious owners want to live in the proposed mansion as their family home.

It is not known who owns Athlone House but it is thought to be a foreign billionaire’s family.

He said in an opening statement that the proposals are for a house of “outstanding architectural quality and worthy of its situation” close to Hampstead Heath.

“Any value in the house as it stands would be readily outweighed by the other benefits,” Mr Purchas told the inquiry.

It is estimated that the developers have spent in the region of £1million on appealing to the Planning Inspectorate to push proposals through after Camden Council failed to rule on the plans in time last year.

The local authority later refused the proposals at a planning committee last summer.

The inquiry is due to run for 12 days over three weeks at the Wesley Hotel in Euston Street, Euston.