Eastbourne's art gallery is set to reopen this spring in a smart new building in the centre of town. Charles Darwent dons his hard hat and takes a tour.

I'll admit to going along to the new Towner Art Gallery with a degree of hesitation, or maybe two. Back in the 1965, having great aunts in Eastbourne was required by law and we, obediently, had Aunt Doll and Aunt Nan. On family visits, Aunt Doll, pretty and gentle, would take me to the old Towner, an early Georgian manor house full of Raviliouses, Hitchenses, bits of Roman pottery and flint arrowheads. Aunt Nan, more robust, thought small boys needed bracing walks and to see what she boomingly called 'the nigger minstrels' at the Congress Theatre. On one never-to-be-remembered occasion, I was called onto the stage by one of these. A timid child, I burst into tears and had to be led, sniffing, into the theatre car park. To the very spot, as it happens, where the new Towner Art Gallery now stands.

So I had two problems with the curved white walls of Eastbourne's re-born art space. First, they were not the red brick walls of the old Towner Gallery; and, second, they appeared to grow out of the Congress Theatre - which, in fact, they do. Given her loudly held views on the theatre's architecture - think the most brutal of sixties concrete brutalism - I can only guess what Aunt Nan would have had to say about Rick Mather's new neo-Deco pavilion: it probably wouldn't have included the words 'elegant Postmodern pastiche'.

But then Aunt Nan and Aunt Doll and their kind are all long gone, which is why the new Towner looks as it does. Talk to Matthew Rowe, the gallery's Director, about the Eastbourne of today and you will deduce a very different place from the tea-shoppe town of 40 years ago. Then, Eastbourne was all WRVS fetes and cream horns at Bondolfi's; now, it is social exclusion and problem estates, young offenders and outreach programmes. In 1969, the borough ended neatly at Hampden Park. In 2009, Eastbourne has spilled out eastwards over once-green fields to Polegate and Pevensey and beyond.

With urbanisation have come urban problems: the town's Devonshire Ward now has a higher per capita rate of heroin addiction than the historically sinful Brighton. Rowe has long been of the mind that art has a part to play in solving these problems, but when he took over as the Towner's Director in 2001, it became clear that a listed Georgian manor house was not the best place for addressing them. The gallery had put in 80 years of sterling service, but it was hidden away in the stately Old Town and had panelled rooms that couldn't be expanded or changed. If art was going to take on the challenges of a new and complex Eastbourne, then it was going to have to do it somewhere else.

Thus Rick Mather Architects building, which is next to Eastbourne's twin theatres but also close to the more demotic attraction of prom, pier and shopping streets. At the same time, and inconveniently, the site is on the edge of The Meads, an estate developed in the 1870s by the then Duke of Devonshire and described at the time as 'the unrivalled Belgravia of a salubrious and flourishing health resort'. The area is still home to Eastbourne's rich, elderly and stubborn. If Mather had tried to do a Zaha Hadid on them, The Meads would have risen up as one great-aunt and stopped him in his tracks. And so he did what he does best, which is to design a building that looks as though it has been there forever.

Or, rather, two buildings. From the outside, the new Towner's well mannered west flank follows the curve of the road while doffing a polite cap to the traditions of seaside Modernism - Mather's gallery might be distantly related to Erich Mendelsohn's De La Warr Pavilion, say, just down the coast at Bexhill-on-Sea. The building's front, clad in zinc, continues the line of the Congress Theatre's glass facade. (Doubtless confirming Aunt Nan's fondly-held belief that the world was going mad, the 1963 Congress is now listed Grade 2*.) As Matthew Rowe points out, Mather's new Towner is not an architectural statement, and nor is it meant to be. Financed partly by the Lottery and partly by the sale of the old gallery, the project had a tight budget of £8.5 million. It also had to look modern enough to lure in a new generation of Eastbournians without looking so very modern as to scare off the old one. The result is an Hercule Poirot of a building, with the Belgian's clever charm but without the waxed moustaches.

Step through the door, though, and you fast-forward 30 years. If the Towner's facade looks like 1933, its ground floor is c.1963 - the year that the Congress Theatre was built. There is a good reason for this resemblance. During the winter months - a lean time for art galleries, but a good one for conference centres - the gallery's ground floor space opens through into the theatre, which, as its name suggests, doubles as a congress hall. The Towner will thus be able to pick up useful pin money by wining and dining delegates. In the art viewing summer, the sliding walls between the two buildings will be closed, thus freeing the space for temporary exhibitions and, incidentally, keeping out stray Black and White Minstrels.

This ingeniousness carries on upstairs. The new Towner's logo is a folded-paper T, and it suits every space in Mather's gallery can be transformed into another space, and each of these spaces has at least two uses. Thus the 400-square-metre first-floor gallery is earmarked for the permanent collection - those Raviliouses and arrowheads, plus ceramics, a station clock and various other et ceteras - but can also be annexed for larger-scale temporary exhibitions. (Rowe intends to use a £1 million gift from Art Fund International to acquire contemporary art works, and these tend to be on the big side.) A store for the permanent lent collection doubles as a research area where visitors can pull out two-dimensional works on sliding partitions. Access is the keyword of the new Towner, and Mather's box-trick of a building is designed to provide just that. Local people were invited to vote for their favourite pictures from the permanent collection.

But the Towner's Director intends his gallery to be accessible in other ways as well. The old Towner's brief was to collect and show work of local interest: Ravilious was an Eastbourne boy, and the pottery shards and arrow heads were fossicked from the South Downs. Rowe realises that the kind of public attracted by these things - think Aunts Nan and DolI - tends to be older and shrinking. To get in the alienated young families who make up the new estates, he needs to offer something groovier.

The Towner's opening programme will thus include the work of a local artist, but a deeply funky one: the Goldsmiths-trained Jodie Carey, whose fluffball chandeliers wowed critics when they were first shown in 2006. The large downstairs space will host a show called the People's Choice, for which local residents were invited to vote in their favourite pictures from the permanent collection, from categories that included seascapes, landscapes and works by contemporaries such as Julian Opie and Olafur Eliasson. And, of course, Eric Ravilious. If all this makes the new Towner sound a tad worthy, then style hasn't been lost to civic mindedness. For all its foldability and tight budget, the gallery has the kind of Licht, Luft und Sonne beauty that Mendelsohn himself might have admired. With quiet insistence, it turns its back on the obvious Eastbourne view (ie down to the sea) and instead looks inland. Its front-to-back central corridors open onto the famous tennis courts at Devonshire Park, while windows in the west wall - these include all one side of the gallery's lift - face a sweep of High Gothic red brick rising up to the bowl of the Downs. You feel that the new Towner has a real sense of Eastbourne, that it gets what the town is about. I'd guess that the feeling will be mutual.

Towner Art Gallery, Carlisle Road, Eastbourne, East Sussex
01323 415441

The museum will open to the public around Easter, and it is anticipated that it will be open six days a week. In addition to presenting changing displays of its permanent collection, it will mount five major exhibitions a year. The programme will include shows by national and international contemporary artists as well as by emerging British artists, and there will be an annual historical art exhibition. Admission will be free, although there will be an entry fee for one exhibition a year.