Old manors, stately piles and rambling country mansions are regularly converted, modernised and turned into new homes. However, such overhauls no longer stop at the brickwork. Increasingly, the surrounding gardens are benefiting, too.

“Gardens and grounds are getting a much higher profile,” says Virginia Hinze, regional landscape architect for English Heritage. “The setting of buildings is now seen as part of their value. Better developers now expect to deal with the garden and grounds as well as the building.”

Rather than being covered over with tarmac for more parking space or an extra housing estate, many neglected gardens are being renewed — usually to their original design.

“It is a growing trend,” says Colin Nicholson, development manager for Octagon, a housebuilder. “English Heritage, conservation officers and local planners want the history of the area reflected in the landscaping, which means the right garden for the right house.”

Nicholson is converting 19th-century Gordon House, on the Thames in Richmond, southwest London. The Grade II*-listed building’s 17 rooms are being turned into three homes, while the garden — circa 1832, with formal hedging and a lake — is being renewed.

“Gordon House is unique,” says Nicholson. “We could not build in front of it, and instead had to put in a formal garden that suited the house. The garden is built over the car park so cars do not upset the view.”

Agreeing to reinstate the garden also helped Octagon obtain planning permission to build five- and six-bed homes — St Margarets Villas at Richmond Lock, ranging from £1.65m to £3m — within the 14-acre grounds, which will be landscaped.

Witanhurst in Highgate, on sale for £32m, may be the second largest home in London, but, says Grant Alexson of Knight Frank, “the garden is more important than the house. The local council wants the house back in residential use and the garden restored.”

Wealthy as any buyer of Witanhurst will be, landscaping and maintaining a large garden is not cheap. Alexson recently had a quote to landscape a quarter of an acre in another Highgate home: it included garden design, irrigation, lighting and installing a stone driveway. The cost was the same price as a small London flat: £120,000.

However, a garden, particularly in the overcrowded southeast, can add up to 10% to the value of a house, says Robert Cornthwaite of Kinleigh Folkard & Hayward, who has marketed homes in Park Hill House in Streatham. Once the home of 19th-century sugar magnate Sir Henry Tate, the house and mews have been converted into 11 homes with six acres of landscaped grounds. “The large communal parkland is gated off,” says Cornthwaite. “It is popular with families because children can run around safely.”

Multiple ownership can bring other problems. “One of the biggest threats to historical gardens is fragmentation of ownership,” says Hinze. “With no clear control, you get individual owners not appreciating there is an overall design and misplanting.”

However, that should not happen at Grade I-listed Dropmore House in Taplow, Berkshire. It is to be developed with the construction of 54 properties, with 11 flats in the main house, on the 220-acre site, which has one of Europe’s finest collection of pine trees. Planning permission for the development is contingent on a landscape management plan and maintenance fund being created for the grounds.

“The gardens have helped to preserve Dropmore. It’s a reciprocal arrangement,” says George Kalopedis, a director of Papa Architects, the project architects. “The buildings would not have seemed so important if it were not for the unique grounds and their setting.”

Dropmore House, Papa Architects, 020 8348 8411, www.papaarchitects.co.uk; Octagon at Richmond Lock, 020 8744 4320, www.richmondlock.com; Witanhurst, Knight Frank, 020 7431 8686, www.knightfrank.co.uk

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