Plans to dig a 13-room basement under a landmark Grade II listed farmhouse in Hampstead, immortalised by painter John Constable, have caused an outcry from conservationists and divided neighbours.

Grove House, which adjoins the grand neighbouring Admirals House, in Admirals Walk, and dates back to 1700, was home to author John Galsworthy from 1918 to 1933 who penned his famous Forsyte sagas there. It has been painted by Constable three times.

Scenes from the Mary Poppins movie with Dick van Dyke were also filmed in the associated Admirals House.

Grove House’s new owners, Caspar and Celia Berendsen, have applied for permission to demolish part of the building, once a service wing to Admirals House, and replace it with a new two storey side extension and rear extension, orangery and outbuilding and to dig a huge 13-room basement.

The plans, from NA architects, aim to “provide a more comfortable living environment for the applicant and his large and young family” and “to deliver a 21st century family home”.

It is claimed the scheme will “bring the historic main building closer to the original design” with most of the extension hidden underground.

But John Gardiner, who has lived in adjoining Admirals House for 28 years, said: “This would be a disastrous destruction of Hampstead’s, and indeed London’s, historic heritage.”

He said: “The sheer scale of the development creates a new mansion destroying the characteristics that presently remain of an early farmhouse.”

He also points out that, along with building works to nearby Fleet House, the area will see months of heavy construction.

Actor Tom Conti, who lives in Hampstead, also objects to the plans. He said: “I’m radically opposed to basements on the grounds of inhumanity to those in the area of construction.”

Two other neighbours, however, support the Berendsen’s application.

Peter and Naoko Rading, of Fleet House, said it was not an overdevelopment. “We understand their needs as a large family,” they wrote.

Two other neighbours, of Upper Terrace, described it as “a good example of sustainable, sympathetic redevelopment of a listed property”.