Turner at Petworth
Great House, Lovely Light - no wonder Turner was inspired, writes Rebecca Rose

Joseph Mallord William Turner, like many a Londoner, enjoyed nothing more than getting away from the smoke for a hearty walk. It was largely thanks to his love of country rambles that he became known as a painter of sea and landscapes - not a natural genre, perhaps, for someone raised by a barber in Maiden Lane in the 1780s.

Turner's long solo walks took him as far as Scotland in the north and Cornwall in the south. Despite his famously squat stature, he often covered about 25 miles a day, subsisting on whatever he could fit into a hanky, tied, Dick Whittington-style, to a stick.

One of his favourite country boltholes was Petworth House in Sussex. A National Trust property since 1947, Petworth's sumptuous 720-acre parkland, designed by Capability Brown, is open to visitors all year round - as it was in the 1800s - and is free to visit. With the recent opening at Tate Britain of Turner & the Masters, a turn around the extensive grounds is a fine way to get into the romantic spirit and appreciate some of the same views that roused Turner 200 years ago.

In Turner's lifetime, Petworth was a long, bumpy coach ride from London, so, once there, he would stay several nights. Today, you can leave Victoria station after breakfast and be at Petworth in time for elevenses, before striding out.

At the end of the 18th century, Petworth was owned by the 3rd Earl of Egremont, a libertine said to have sired 40 or so illegitimate children, who also had a keen interest in contemporary British art. The work of the young Turner caught his eye at the Royal Academy's annual exhibition and he commissioned him to paint a country house portrait in 1809. On his ensuing visits to Petworth, Turner delighted in the earl's inherited collection of Old Masters, in particular a striking work by Claude Lorrain - an influence now explored by the Tate's show.

When he wasn't making sketches from the earl's collection, Turner roamed freely in search of inspiration, often stepping out at sunset. From the house, there is a marvellous view of gently sloping parkland which stretches to the horizon, punctuated halfway by a large fishing lake, silvery in the September sunshine. It is an altogether brighter aspect than Turner's moody, crepuscular studies. These small-scale gouache works painted on site foreshadow the plein air painting that exploded half a century later.

Striking out further into the grounds, I spy small groups of deer wandering around somewhat warily (the rutting season, now in full swing, was about to begin). This scene has an intriguing echo inside the house. In an unassuming spot in the grand dining room hangs a fiery sunset painted by Turner in 1827, with a gathering of fallow deer roaming in the foreground. This was the view of the park from the dining-room window, commissioned by Egremont so that dinner guests facing away from the window could survey the same view as those opposite.

In the mid-ground, a game of cricket is being played, presumably by locals, who were also allowed to use the park. This was doubtless included to suggest the earl's magnanimity - as well as his interest in sport. Several of Turner's gouache sketches point to other forms of public activity in the park -picnicking by the lake, horseriding, and so on. On my afternoon stroll, however, I came across even fewer walkers than deer. In fact, aside from a large flock of geese, I was virtually alone. But instead of the slight unease one can feel on a solo ramble in the countryside, I felt perfectly safe in Capability Brown's benevolent haven. The dull roar of the dual carriageway was the only reminder that I was still in the 21st century.

In this same harmonious painting, in which man and nature coexist so peacefully, Turner - who became known as "the painter of light" - perfectly captures the liquid gold of the dying sun reflected in the lake. He had plenty of time to observe the effects of light on water in this particular spot, as when he wasn't painting in the grounds, or barricading himself in his studio in the main house, he was to be found fishing. These days the lake is full of carp and tench; it is possible to fish, but anglers must obtain permission.

In another oil commissioned by Egremont, Petworth House is viewed from the far side of the lake. In an attempt to make his patron's estate look even grander, Turner featured a Dutch-style fishing boat in the foreground, a scaling device designed to make the house recede further still, giving the impression of an even larger estate. It is a reminder that these works served a purpose beyond capturing the natural surrounds.

When Capability Brown redesigned the grounds between 1751 and 1764, he manipulated the terrain to provide the grandest, yet most natural-seeming vistas. He extended the lake, at great expense, and the wall of the estate, to give a greater impression of space. He also planted trees in fashionable clumps, so as not to mar the view. Only a few of those remain: more than 700 were lost in the storm of 1987. It is a small but comforting compensation that new life has sprung from this loss; 283 types of fungi have been found on the remaining stumps, as well as several rare varieties of beetles.

In Turner and Egremont's day, the park at Petworth was also famed for that most dramatic of birds, the raven. Alas, they disappeared 160 years ago. Until earlier this year, that is when a single raven was spotted by Petworth's head gardener in one of the very spots that Turner depicted nearly 200 years ago.