Geoffrey Mead of Sussex University's Centre for Community Engagement is wearing his trademark trilby. It's black, matching his long overcoat, and endowing him with a suitably noirish appearance in his role as guide for a tour of Brighton's "Greeneland" – the area of town whose 1930s razor-toting gangsters inspired one novel and two films. The latest cinematic interpretation of Graham Greene's Brighton Rock has been increasing the demand for Mead's specially adapted tours of his home city.

Mead is well qualified to truffle out the hidden alleyways, the murky, unconsidered corners and the legacy of long-gone slums. He combines the knowledge of a native of 61 summers with the academic rigour of an MA in local history. He lectures on landscape studies and has just completed his doctoral research into the changes that occurred in and around Brighton during the inter-war years. His tour helps to explain how Greene, a Catholic convert, came to present prewar Brighton as a purgatory of cheap thrills and transitory pleasures with something literally and metaphorically deeper lapping relentlessly against its shifting shoreline. Also how a city that has a reputation for being open to trends and pleasures of all kinds hasn't changed quite as much as its outward appearance might suggest. "That mixture of glamour and sleaze, innocence and criminality is still there," he says.

Mysterious fires

The great old West Pier is no longer there, only its charred skeleton. Also gone is the luxurious Bedford Hotel, thought to be the model for the Cosmopolitan where Greene sets up the meeting between the suave London mobster Colleoni and Pinkie Brown, small-time local gang leader and aggressively precocious product of the crammed and stinking streets that once tumbled up the hillsides just off the London Road. "The Bedford, too, was a victim of one of Brighton's mysterious little fires," Mead reveals, having just retrieved his trilby from the effects of a powerful sea breeze as we approach the Palace Pier.

The Palace has changed beyond recognition since the 1940s when the Boulting Brothers first filmed Brighton Rock. So has the stretch between the two piers. Beach bars, clubs, restaurants and even galleries now line the front where mods and rockers once fought their pitched battles. In search of more period detail, Rowan Joffe, director of the latest film of Brighton Rock, chose to film in Eastbourne as well as shifting the action from the 1930s to the 60s. Mead can talk about that era with some personal experience. "I used to ride my Lambretta along the front in my fur-lined parka," he grins. "But my mum insisted that I wear a crash helmet and she made sure I was out of the way when the gangs came down from London on a bank holiday."

A formidable woman, his mother was a cleaner and his father was a lorry driver. Young Geoffrey passed the 11-plus but hated grammar school. Despite scraping five O-levels together, he left at 16 and took menial jobs in supermarkets. "But I loved walking on the Downs to get away from strip-lights and deep freezers," he recalls. "In 1977, I went to a night-school course on the making of the Sussex landscape and I was transfixed." Three years later, he made it to Sussex as a mature, unqualified student at what was then the Centre for Continuing Education. "I just fell into university life," he goes on. "I was being paid to read books and I loved it."

So much so that he went on to join the staff. Financial restrictions, including cuts in government funding for second degrees, have caused some universities to discontinue their commitment to continuing education. Sussex has chosen instead to change its emphasis. Along with degree courses, it also offers shorter introductions to higher education. As the new name suggests, the Centre for Community Engagement is a way of bridging the gap between the campus, the city and the county beyond. Mead was able to consult with colleagues such as Professor Fred Gray, an expert on the social history of seaside resorts, and his walks are a good example of how academics can shed new light on familiar settings for residents and visitors.

I find my knowledge of Brighton and appreciation of the novel enhanced from the moment we step out of the city's handsomely restored and soot-free station. Packed trains from London were disgorging passengers here on the fateful Whit Monday of the novel's gripping first page.

Greene was researching Brighton Rock as the slum clearance programmes of the mid-1930s were under way. Mead suggests that he could well have witnessed the demolition of streets that spawned Pinkie and Rose, the drab, doomed waitress who marries him. Now covered with social housing, these hillsides behind London Road would have been crammed with properties thrown up by speculative builders in the 1820s to accommodate the families pouring into Brighton from the surroundings areas. "There was a big Catholic-Irish population as well," my guide points out. Rose and Pinkie's Catholicism is the one thing they share with the author.

As we stroll back through the Old Steine, with its 1930s bus shelters, Mead reminds me that the ambitious Pinkie had moved away to the west side of town. "Then and now that borderland with Hove has always been a zone in transition; a place for drifters where nobody asks any questions; a place of bedsits and dark alleyways off handsome squares."

East side

We're still on the east side but, as if on cue, we come to a narrow alley behind the Royal Albion Hotel. A kitchen worker taking a cigarette break behind one of the restaurants on East Street eyes us suspiciously. This has evidently been a spot for nefarious activities since long before Greene breezed into Brighton. There's a telling contrast between its seediness, the crested frontage of the hotel and the welcoming interior of the restaurants.

I find myself contemplating one of Mead's observations about the British resort "with its veneer of sophistication" being a "vehicle for a shifting underclass". That's one thing that hasn't changed since the 30s, he would argue. "The geographical settings are backdrops to the story and not essentially part of the plot." But being shown around what remains by an academic steeped in community engagement can illuminate a 1930s novel as well as a film that reimagines 1960s Brighton in 21st-century Eastbourne.

Historical tours by academics are not on every university's list of essential projects, but Mead believes they make good adjuncts to existing courses and are also a way to engage a community in the work of a university.

"They are not for everyone to do as you need to be able to work in the open with no notes in all weathers, and importantly be a bit of a showman," he says.

Sadly, though, "community education in higher education seems to be a fading flower these days".

• Geoffrey Mead can be contacted at g.mead@sussex.ac.uk. His tours last around an hour and a half and cost £30 for groups of up to six.