In 2005 Jeremy and Jessica Sokel, who are both solicitors, bought the £2
million 1950s house next door to Mr Alderton’s Grade II-listed Arts and
Crafts home.

The Sokels, who have two young children, knocked it down and rebuilt it as a
modern glass-and-brick three-storey block. In 2007, they purchased the next
house along for around £1.5 million, intending to demolish it as well.

In 2009 Mr Sokel, 50, and Mrs Sokel, 46, were given approval to construct
another futuristic three-storey house there and install swimming pools 16ft
beneath the gardens in both properties.

Mr Alderton and his wife, both 70, challenged the decision but were
unsuccessful.

It meant that when his neighbours, Rosthchild investment banking executive
Alexander Midgen and his wife Karen applied to knock down his
newly-purchased £2 million home to replace it with a far larger house for
them and their three children, Mr Alderton was determined to stop the
development.

Mr Alderton and Mrs Collins complained, saying that the whole scheme would
mean concreting over a green space and creating a new house on the site two
and a half times the size of the existing red-brick home.

They said it would damage their enjoyment of the Grade-II listed Arts and
Craft home where they have lived for 35 years.

This time the couple were successful as Camden Council rejected advice from
planning officers to allow the scheme and refused it permission to go ahead.

Councillors said they had no option but to reject the application as the new
building would be closer to Mr Alderton’s property and would alter the
setting.

“If this had been granted, it would have sent a signal to developers
saying, ‘come and make a quick buck by knocking down our historic homes and
digging out huge basements’,” claimed Mr Alderton, the son of a
Lincolnshire carpenter.

He complained that his street in a conservation area in Hampstead, had seen 18
applications for major building works in just two years.

“I bought my house 35 years ago and it was run down,” said Mr
Alderton, who became a household name in the Sixties with his portrayal of a
hapless teacher in the sitcom Please Sir!

“I put it back to its original state. I was going to be an architect
before I started acting, so I put it right, and then it became listed. I did
not feel I needed to build a basement or put in a lift.”

Mr Alderton’s house was once owned by the sculptor Hamo Thornycroft, who
designed the statue of Oliver Cromwell at the Houses of Parliament, and
includes his signatures on window panes.

He and his wife met on the set of Upstairs, Downstairs, on which he played the
chauffeur Thomas Watkins and she was the maid, Sarah.

He said he hoped that his victory would mark a sea change in attitudes to
homeowners expanding their properties below ground.

“This sends out an important message about what people can and can’t do,”
he said.

“I want people to sit back and relax and enjoy their homes as they are.”

Digging under homes and gardens to build swimming pools, garages, squash
courts, gyms and even diving pools, has become increasingly popular in
affluent parts of London where space is at a premium – often to the ire of
neighbours.

Nigella Lawson, the television cook, and her husband, the art dealer Charles
Saatchi, were reportedly so incensed by a planned garden conversion next
door to their £30 million flat in Belgravia that they decided to sell up.

Mr Alderton’s prominent fellow residents in Hampstead include Tom Conti, who
starred opposite Collins in the film Shirley Valentine; the controversial
television presenter Jonathan Ross; and Ken Loach, the Left-wing film
director.

Mr Midgen declined to comment. Dusan Savic, of Design Solutions, the firm of
architects which had worked on the proposed development, said: “I am
surprised by the decision, as it was recommended by planning officers.

“We have two options: to appeal or to rethink the plans so the new building
does not come any closer.”