An ostentatious family mansion which could replace a beloved Victorian old hospital would be better looking than many of the “pumped-up” giant homes in Hampstead and Highgate, it has been argued.

The mysterious owners of Athlone House in Highgate on the edge of Hampstead Heath have denied claims that their proposal to demolish the house and replace it with an eight-bedroom home would harm the area’s character.

Expert architect Peter Stewart told a planning inquiry last week on behalf of developers Athlone House Limited that plans are to swap one “ambitious house for a wealthy person” with another.

He argued that the mansion would be far better designed than the many “giant, executive homes” nearby.

Mr Stewart told planning inspector Colin Ball: “There is a kind of bad, very large house that gets built, which I suppose I would characterise as a sort of giant, executive home.

“It looks like a small house which has been pumped up to a large size by a bad architect.”

He went on to add that the proposed classical-style mansion with basement car park, opulent landscaped grounds and a swimming pool is an “appropriate ambition” for the site, the 12-day inquiry heard last Wednesday.

Campaigners have previously likened the proposed designs to a “Stalinist wedding cake” and an “Arabian nightmare”.

They are urging the Planning Inspectorate to refuse the developers’ appeal against Camden Council’s decision last summer to refuse the proposals.

They also want developers to stick to a historic agreement known as a section 106 agreement obliging them to refurbish the house to its former glory.

However, Athlone House Limited have contested that the mansion cannot be restored because the necessary repairs are too extensive.

The inquiry heard that the owners were told by legal advisors that they were under “no obligation” to refurbish the house.

One of the many concerns raised by the 5,500 campaigners fighting to save the former RAF intelligence base is that the proposed mansion is bigger than the current footprint of Athlone House.

Last week, eminent architect Professor Robert Adam, who drew up the designs, offered reassurances that the replacement home will not look any bigger to passers-by.

He said: “Someone coming to Athlone House who disappeared for two years while it was being constructed and looked up, looked across from any public position, they wouldn’t say, ‘Oh my gosh, that’s a much bigger building.’”

He later added that the owners, thought to be the family of a foreign billionaire, did not want to build something “elaborate”.

Prof Adam said: “It wasn’t a two-up two-down but it wasn’t Buckingham Palace either.”

The inquiry continues until Friday (tomorrow).