Filming the day when the foreigners left the Fens

So what would happen if you replaced immigrant workers with jobless British ones? Evan Davis reports on an extraordinary experiment

If you stand outside the Muppet Inn in the main square of the market town of Wisbech in Cambridgeshire, you don't have to try very hard to hear a negative view of the immigration that has changed the area over the past few years.

Since the enlargement of the European Union in 2004, thousands of central and east Europeans have migrated to the East of England, and the Fens in particular. Perhaps that is because there is a tradition of seasonal agricultural work; perhaps it's because there is plenty of space. Whatever the reason, you might think it flattering to Wisbech that of all the places in the world the Poles could have moved to, they chose that particular town. That's not how all the locals see it however.

Indeed, the views you sometimes hear in Wisbech about the new arrivals are often of a form that capture the very dilemma broadcasters face in covering the whole subject of immigration. On the one hand, good television needs strong views, passionately argued. In Wisbech and elsewhere, you'll find those aplenty on the subject of foreigners settling in our country. But on the other side, programme-makers are naturally shy about unleashing extreme views, intemperately expressed. And often on a subject that is taboo, it is the people with those views who often most want to speak.

TV schedulers are undoubtedly keen to tackle the subject, but only if imaginative ways to do so can be found which are engaging and non-inflammatory. It is a high hurdle to jump. Which is where Wisbech comes in.

It was Leopard Films which first approached the BBC with one particular idea, for an ambitious programme that could explore the impact of immigration on Britain through the medium of what one might call an "alternative reality show". The programme would create an alternative world for a week, in which immigrants were taken out of Wisbech for all to see how shops, factories, schools and clinics functioned without them.

OK, it was never going to be quite that dramatic. You couldn't change the demography of a town. But the programme would focus on scenes in Wisbech life. And its key conceit would be a job swap: the placing of local unemployed into workplaces left short of staff once migrant workers had been removed.

To me it sounded like a fantastic idea. You often hear the argument made that British jobs have been stolen from us by foreigners. What a great chance to put the thesis to the test. The BBC liked the idea as well; there was just the small matter of getting it set up and filmed. That was all back in 2008. The result will finally be aired on Wednesday.

It's fair to say that is has been a tortuous journey, and that meeting the exceptionally exacting standards of balance and reasonableness which the subject demands turned out to be far more challenging than anyone involved had realised. For one thing, many of the original ideas had to be toned down. And at almost every step in the construction of the programme, the producers – who have spent far more time in Wisbech than me and got to know the town's people better than they could ever have imagined – were left with difficult challenges.

The main issue in the film was always going to be the labour market, especially the low skilled end of it. This was indeed why Wisbech was such a good place to come. It has been depleted of its middle class in recent decades, and is surprisingly one of the country's more deprived areas. The large Waterlees neighbourhood is a classic example of that phenomenon, inner-city problems outside the city.

So it is here that you find the folks who have arguably felt the harshest negative effects of immigration: the long-term unemployed; the people who struggle to find a job faced with the competition of motivated, cheap, hard-working foreigners.

But to find the right panel of participants was not easy. There are plenty of people who struggle to get a job. But it turned out that many of the long-term unemployed are difficult to employ. Perhaps we shouldn't have been surprised at this.

To put into jobs those with the least hope of ever working and then filming them would bias the programme against the British worker; however, to select only the most driven Brits among the longer term unemployed would have given a wholly unrepresentative picture too.

Being a touchy subject, immigration and employment is not an issue on which you can be cavalier about the overall balance of the cast. And it took months of effort, and hundreds of conversations with local people, for the producers to find a varied group of a dozen or so who could be placed in jobs for a couple of days. And even that doesn't mean all problems were overcome.

The worst employers, exploiting gangs of immigrants, don't feature and were never going to. At the other end of the scale, many moderate people and good employers were reluctant to talk about the subject. An article in a red-top newspaer, based on an undercover reporter's apparent exposé of sex in the strawberry fields some years ago had led some to doubt the media's seriousness of purpose.

And we often encountered people whose views on immigration seemed to have been framed by what they have read in the papers, rather than their own experience. You don't really want a film simply to regurgitate views that have been picked up from elsewhere.

So there have been plenty of snags. But the film is still truly and surprisingly informative. Anecdotal the evidence maybe, but for me – one who is used to using statistics to make a judgement – a dozen specific cases have revealed more than any number of charts or tables.

"The Day The Immigrants Left" will be broadcast on Wednesday at 9pm on BBC1