Greenery is a benefit increasingly sought after - at a price. "We have seen a definite trend of both prospective buyers and tenants looking for properties where they can see trees and gardens, or where they have outside space such as a terrace or patio," says Nicholas Hurst, of the Pimlico estate agents Moreton's. "Even a glimpse of a few branches currently puts a premium on the price of a property."
"We have people coming in with an absolute requirement that they can overlook the greenery," confirms Philip Castle, of Sovereign House Estates of East London, whose office deals with property in Victoria Park. It seems that they are also willing to pay for the privilege.
"A typical four-storey, four-bedroom family house overlooking Victoria Park or the common would sell for around pounds 300,000," - representing a hefty 25 per cent premium over the price of similar properties in the vicinity without the extra "green" feature. "There is obviously not a huge amount of greenery around here," says Mr Castle. "So these properties have real scarcity value."
Apart from offering solace from the stresses of urban life, ("greenery provides much-sought-after peace for residents from the din of urban life," says Moreton's Mr Hurst) - warmer summers, notwithstanding the present lacklustre one, and the need to walk pets are among the factors that are apparently encouraging buyers to put "outside space" on their list of priorities when choosing a property.
Birkenhead Park, in Wirral, Merseyside, which formed the model on which Central Park in New York was based, illustrates another facet. Wirral Council, which oversees the area, has made a conscious effort to invest in its parks and open spaces, and the Birkenhead one boasts a plethora of events and facilities, from Victorian weekends to upgraded cricket pitches.
It means that the park affords something over and above mere access to grass and trees - a broader sense of a thriving community life. Many of the Victorian and Edwardian houses nearby have been converted into flats.
"While property prices are relatively modest - you can pick one up for around pounds 20,000 - with a view over the park itself the price rises to pounds 25,000 or pounds 30,000," says Sue Taylor, of the agents Jones and Chapman.
But what if you are unwilling or unable to pay the property "green premium"? If you are prepared to compromise and have class proximity to, rather than a vista of, green leaves, you can save on cost. In Blackheath, south- east London, for example, a flat with a view over the heath recently commanded pounds 280,000, but you could buy a similar property that still has convenient access to the heath for pounds 20,000 less, according to Marc Williams, of Blackheath's estate agents Kinleigh, Folkard and Hayward.
You may, however, be looking for your own individual piece of rus in urbe. David Ryan, of Alexander's in north-west London, has noted a desire on the part of many purchasers "to have their own exterior personal space". But that luxury also comes at a price.
"Buyers should expect to pay around pounds 10,000 to pounds 15,000 extra for a flat with a roof terrace or small private garden in this area," says Mr Ryan. John Garswood did so, purchasing a flat complete with a roof terrace at the end of last summer. "I had always been in flats with no outside access, and it really began to get me down. I was determined I wouldn't spend yet another summer in a hot, sticky city, cooped up inside. The extra money was definitely worth it for me."
There are plenty of "unofficial" roof terraces around, so when purchasing a property that already has one, you or your solicitor need to ensure that planning permission was originally obtained.
Should you have a suitable potential site for your own roof terrace, local authority approval will be required to ensure that the project complies with building regulations, and issues such as the possible objection of neighbours, as well as safety provision including secure railings, all need to be dealt with.
Bonita Bulaitis, of Channel 5's Virgin Gardeners series, suggests using the services of a structural engineer or surveyor.
"Drainage is particularly important, or you can end up flooding your flat," she says.
If, however, you can clear these hurdles, you can end up with a desirable piece of outside access, while also adding value to your property.
For decoration: "Plant slow-growing trees in lightweight compost," advises Ms Bulaitis. "Grasses can also help to filter the wind."
"It can get a bit blustery on the terrace at times," agrees Mr Garswood. "However, at least I can come home from a day's work, throw open the door that leads on to the terrace and sit back and relax.
"This is my own green haven," he adds, "and I could not go back to an `enclosed' flat."
Estate agents: Alexander's 0171-431 0666; Jones and Chapman 0151-608 2287; Kinleigh, Folkard and Hayward 0181-852 9451; Moreton's 0171-932 0101
Bonita Bulaitis, garden designer 01920 466466