UNDERGROUND streams and heavy traffic will be the rallying cries of campaigners at a meeting tonight to decide the fate of a Grade II-listed Highgate mansion. Witanhurst was bought by private developers more than two years ago. An extravagant redevelopmen

UNDERGROUND streams and heavy traffic will be the rallying cries of campaigners at a meeting tonight to decide the fate of a Grade II-listed Highgate mansion.

Witanhurst was bought by private developers more than two years ago.

An extravagant redevelopment project that will see the building's old service wing razed to the ground will be considered by Camden Council's development control committee.

Campaigners have broadly welcomed the developers' pledge to restore the dilapidated manor house. But there are concerns over the scale of the work, which will include an enormous underground excavation.

Although the property is earmarked as a family home, it would include a nine-metre deep basement housing a 33-seater cinema, a swimming pool, a gym, a spa and a wine cellar, staff quarters and an underground car park.

The service wing would be demolished and replaced with a two-storey "orangery" extension providing further bedrooms and living space.

Highgate Society member Michael Hammerson said: "We are particularly worried about the effect the basement excavations will have on underground water bodies.

"This excavation is so big that it has to have a major impact. We must see more evidence about what's going to happen to the water."

The City of London Corporation has written to the council to comment on the lack of information about the effect of tampering with the area's underground water flows.

The Highgate Conservation Area Committee has also raised concerns over potential safety issues caused by pedestrian diversions and vehicle movements.

If approved, the three-year scheme would require a new driveway from Highgate West Hill for construction vehicles. This would then become a second permanent access to the house.

Planning Potential, the company representing Witanhurst's mystery owner, has submitted a note to the council ahead of the meeting.

The group claims that the application to dig the vast basement is supported by full hydrological studies and that there will be no change in underground water flows off-site.

It says English Heritage has agreed to the removal of the service wing to make room for the orangery.

And it adds that it is unfortunate but inevitable that the major works needed to repair 40 years of neglect would cause some initial construction disturbance - but this is an investment in the future.

The meeting is due to begin at 7pm at the town hall in King's Cross.