Can you dig it?

The answer is a new film, out next month, called Grow Your Own, which centres on an allotment in some unnamed northern city (actually Liverpool, but it could be anywhere) where old boys grow carrots and leeks in neat little rows, and spend their days leaning on spades and drinking cups of tea when they should be getting on with the digging.

It was perhaps inevitable that someone would make a film set on an allotment. With allotments more fashionable than they have been for years, the waiting lists for plots are longer than ever as growing numbers of urbanites wake up to the fact that vegetables do not have to be sprayed with chemicals to within an inch of their lives, or wrapped in plastic and flown halfway round the world before arriving on the supermarket shelf.

Barely a week goes by without some television gardening expert popping up to tell us how to grow fresh 'n' easy salads for summer, or carrots just like your grandfather used to have.

I should know: two-and-a-half years ago my wife and I got an allotment in East Acton, and we have now gone from two people who did not know their pumpkins from their parsnips to a couple of vegetable obsessives who are never happier than when we are out there among the cabbages and turnips.

And, of course, the allotment is probably the quintessential Ealing comedy setting, a place where you will find a matchless gathering of colourful and eccentric characters who represent the perpetual battle of the little man against the faceless machinations of authority.

There is a harder, more modern edge to Grow Your Own than such easy knockabout fun, however. Inspired by a real project set up by a psychotherapist in Liverpool to help asylum seekers, the film is directed by Richard Laxton and coscripted by Frank Cottrell Boyce (24 Hour Party People, A Cock and Bull Story) with Carl Hunter.

It shows what happens when a group of refugees are given plots on an allotment to help them overcome their trauma, and how they fare when they encounter the entrenched values of the traditional English working-class plot-holders (with an avaricious mobile-phone company to add some spice to proceedings).

In short, Grow Your Own is not a film about gardening. But then gardening isn't really about gardening, either; it's about life. Half the people who are down on their allotment at the weekend, digging their potatoes, planting their Brussels sprouts, are not doing it for the fresh fruit and vegetables they will get at the end of it - they are doing it to escape the drabness of their home lives, to get away from the pressures of their job, or to connect in some atavistic way with the seasons and the earth in a way that we, as city dwellers, have fundamentally forgotten.

Such concerns, however, are not normally the province of your average filmmaker. Movie directors, as we all know, hang around places like Soho House drinking skinny lattes and swapping industry gossip: they do not spend their weekends getting dirt under their fingernails and wondering what to do about about the slugs. They know as much about runner-bean trenches as I do about shutter speeds.

It was, therefore, with a certain sense of trepidation that I went to an early screening of Grow Your Own: the risible clichés about allotment life which it was likely to perpetuate were too awful to contemplate.

The first sight we have of the Blacktree Road allotments is an intriguing one. This is no picturebook allotment, with roughhewn beanpoles festooned with sweet peas in among the runner beans; instead it is a rather grim, urban place, with row after row of plots set in the shadow of a huge gasometer. The docks - huge, impersonal - are just around the corner. I have seen some more unprepossessing allotments in my time, but not many.

It is the people that make an allotment, however, and the people who tend the plots at Blacktree Road are as grumpy, maladjusted, obstreperous and downright peculiar a bunch as ever planted a row of lettuces - playing the parts of allotmenteers with gusto are Olivia Colman (Peep Show), Eddie Marsan (Vera Drake), Benedict Wong (Sunshine) and Iranian stand-up comic Omid Djalili. They're typical allotment folk, really.

There is also the cranky Scot who will go to extraordinary lengths to assert his individuality, and who spends his leisure hours watching gardening programmes and shouting at Alan Titchmarsh; the old boy who plants his tomato seeds on Boxing Day and puts them on the television to keep warm; and, at the head of it all, the overbearing committee chairman, Big John (Philip Jackson), who runs the allotment as his own personal fiefdom.

Anyone who has ever had an allotment has probably come across a Big John in their time - the rulebook Mussolini who regards any infringement of the regulations as a personal affront and who considers pristine paths and immaculate sheds as far more important than the messy business of actually growing anything.

Fortunately, the committee members on my own allotment are models of tolerance and understanding, but I have also come across places where a bullying autocrat like Big John would be welcomed as a kindred spirit.

Most of the time Grow Your Own is brilliant on the small details of allotment life, such as the bloke who proudly takes home a bunch of carrots, only to find that his wife really isn't interested.

I am not sure if I have ever come across anyone dismantling a shelf at home in order to make some useful structure for the allotment, but the moment does capture a greater truth: that obsessive allotmenteers never cease looking for discarded bits of junk which can be transformed into a shelf for the shed, or a protective barrier against the wicked carrot fly. For such people, a well-filled skip is the equivalent of the first day of the Harvey Nichols sale, only free.

Then there is tea. Tea plays a crucially important role in allotment life. Assuming you have access to a camping gas ring, or a Thermos flask, tea is the social lubricant which allows allotmenteers to get on with the important business of the day - discussing the state of the world, griping about one's fellow plot-holders, telling terrible jokes, complaining about the slugs/greenfly/bean weevils, and generally doing anything rather than gardening. In Grow Your Own, they drink an awful lot of tea.

Perhaps one should forgive the film's occasional transgressions. The thing that struck me during that first, introductory tracking shot of Blacktree Road was that there was an awful lot of ... grass. Grass? What on earth would an allotmenteer want with grass? Grass, in the shape of silly, prissy little lawns? Which you cannot even eat?

Grass is the enemy, a pernicious weed which invades your plot and upon which allotment-holders expend vast amounts of energy to keep at bay. I once heard of an allotment-holder who grew a small lawn on their plot, for their children to play on, but they were regarded as very peculiar.

Other faux pas are less forgiveable. Without wishing to give away too much, there is a crucial point in the film when the allotmenteers are threatened with losing one of their plots.

They seem to accept this as a fait accompli, on the grounds that the plot is occupied by one of the refugees, and anyway it is only the one plot. But I don't think there is an allotment society in the country which would not have fought tooth and nail for that plot: they love their vegetables, and they love their land, and there is nothing they would not do to preserve their little corner of paradise.

In a curious way, though, the thing that the film gets most wrong is the thing it also gets most right. Before the refugees came along, the Blacktree Road allotments were almost exclusively white and working-class, just like allotments in Britain always used to be. But not any more.

Perhaps there are allotments like that in the countryside, or the outer suburbs - but not in the big cities. These days allotments are full of Bangladeshi, Iraqis, Moroccans, Iranians, Afghans, Kosovans, Italians, Algerians, Poles, Somalis, Turks, West Indians - it is hard to think of a nationality not represented.

Often it is the first-generation immigrants who are the keenest gardeners, growing varieties that hark back to their homeland: there is a West Indian on my allotment who still grows beans that he first brought over from Grenada several decades ago.

Traditional allotmentholders are not yet a minority, although it was quite an eye-opener when I realised that on my tiny site - just 15 plots - my wife and I were until this year the only permanent plot-holders born in this country.

It is this phenomenon which the film captures so wonderfully - even if it does take the dramatic liberty of having the established plot-holders all white, while the foreigners arrive as one multicoloured minibus full of asylum seekers.

And you know what? I don't think I would be betraying any great secret to say that in the end they all get on just fine, just as they do on my allotment.