Next stopski London!

Marcin takes a last swig from his Okocim beer, drops the bottle into a bin and steps aboard the bus. "Next stop London!" he grins and, bending his massive 6ft 6in frame, shuffles towards a seat at the back. His friend Lucasz is already seated, gazing tearfully through the window at his girlfriend, waving from the concourse.

There are many sad goodbyes at the Dworzec Zachodni bus station as the coach to London prepares to leave on its 22-hour journey. The farewells at this grim, communist-era terminal are a daily ritual as dozens of young people board the bus for Britain. Most are heading for jobs they call praca na czarno - work in the black economy.

When 10 countries, including Poland, join the EU on 1 May, Marcin, Lucasz and thousands more like them will no longer be obliged to use time-honoured scams to bypass Britain's immigration and labour laws. They will have an automatic right to enter Britain and work legally.

But has it really been that hard? It was disclosed this week that Britain has operated a secret "open door" policy to east European workers and entrepreneurs for some time. According to whistleblower Steve Moxon, an immigration official, restrictions were relaxed to clear a backlog of cases of those wishing to live and work in Britain.

And the evidence we found in Poland, which supplies a huge army of workers to Britain's underground labour market, is that when border restrictions are lifted on 1 May, it will be business as usual for the czarno employees. Those who want to work in Britain have experienced little difficulty in doing so.

The daily coach from Warsaw will pick up more passengers at towns between here and the German border, including Lodz, Poznan and Slubice. At Dover, an immigration officer will check everyone on board - but it is rare for anyone to be turned back. Between January and September last year just 90 Poles were refused entry out of thousands who arrived.

Marcin explains: "There are no restrictions on us just visiting and if some people disappear into the black economy, nobody seems to mind very much." Marcin is 28 years old, a timeserved carpenter who is heading for a job on construction sites in London.

His story is typical of many who take the London bus. He tells it in excellent English, enriched with a vocabulary acquired on building sites: "I first went to London a few years ago, made some money and came home. But the job I was doing here was paying shit money - less than 75 quid a week. So I'm going back for a while."

In a good week working in London, he says, he can earn £1,000. He lives with friends in Shepherd's Bush and his outgoings are low. On this trip, he is taking his friend Lucasz.

"He doesn't have a trade, but there is plenty of work for labourers," Marcin says.

Nearby, 23-year-old Andrzej is hugging his girlfriend, Anna. They don't expect to see each other for two, maybe three months. He has signed up with a Polish gangmaster hiring out labour to farms in the Midlands. Andrzej, a keen bodybuilder, has been working in a pizzeria for 800 zlotys a month - about £110 - and he wants to earn enough to support himself through a full-time course at a college for public service staff.

He speaks very little English, but he will be living and working with Poles. He spent a few months working for the gangmaster last summer.

"There were 13 other Polish guys, all like me, living in a five-room flat in Birmingham," he says. "We'd get picked up and taken to the farms."

He says the work involved various jobs: tractor-driving, fruit-picking and mixing animal feed. He expects to work very long hours to make up for the fact that the pay rate is low - £2.70 an hour. But even that will enable him to earn nearly 10 times more than he does in Warsaw.

"I'll stick it for four months, maybe eight," he says. If everything works out, Anna will join him in England later in the summer.

But what about the immigration controls? If the port officers at Dover suspect a person is going to work illegally in Britain, they can refuse them entry.

Andrzej is sanguine about the risk. He is carrying a letter from a Polish friend who is settled in Britain, inviting him for a week's holiday. To reinforce the idea that he is simply spending a week in Britain, he has booked his return for seven days ahead. The ticket costs around £65 for the round trip and he is happy to write off half the fare.

The young workers heading for Britain are quite open about the ruses they employ to gain entry. Some buy courses from language schools which, in reality, do not exist. They are bogus colleges that simply provide a document to state that the "student" has enrolled. But most say they are taking a holiday.

Home Office figures state that around 1,500 Polish nationals are currently employed legally in Britain. No one knows how many are employed illegally, but anecdotal evidence suggests the figure is in the thousands. The question that arises from Poland's accession to the EU is, how many more will come?

While all the existing EU members are granting unrestricted entry to citizens of the new member countries, only Britain and Ireland are allowing unhindered access to jobs. This policy has aroused concern that Britain's labour market will be flooded by residents of the poorer central and east European countries and there are fears that many will be attracted to Britain's benefits system once a qualifying period of 12 months' work has been completed.

"I don't think you have too much to worry about, as far as Poland is concerned," says Grzegorz Furniak, director of the Job Pilot recruitment agency in Warsaw. "Anyone who really wants to work in Britain is there already. The others, who are complaining that they have no work, no money, will talk about it but most of them will just keep on grumbling and sit tight. Entry to the EU is not going to make a big difference to that situation."

The statistics suggest he may be right. In 2002, more than 100,000 mainly young Poles left to work abroad. According to a survey carried out by the Polish news magazine, Wprost, most of the people who leave to work abroad are aged below 30 and almost all expect to return within three years.

At the Mlynarska Street job centre in Warsaw's Wola district, staff handle hundreds of enquiries a day, but the average for enquiries about work abroad runs between 15 and 30. In Room 21 on the first floor, where people looking for work abroad are seen, there is a huge noticeboard carrying job offers. There are opportunities for nurses in Holland and the United States; civil engineers are needed in Ireland and farm workers are in demand everywhere.

There is one single advertisement from Britain, offering work for experienced butchers. Most of the people who come here are looking for jobs in Germany or the United States," an official says. The reason, it is suggested, is that these countries have traditionally made it more difficult for people to work illegally than Britain, and workers heading there are more likely to try the official route.

So is Britain perceived as a soft touch - and will Poland's EU accession make little difference to the number of Poles living and working in the UK? I put the questions to Marcin Kulinicz, an official at Poland's Ministry of Economy, Labour and Social Affairs, He has special responsibility for labour and migration at the ministry's Department of European Relations and has been closely involved in research about how many Poles will move abroad after 1 May.

"The general opinion here is that there will not be great numbers," he says. "While quite a high percentage of young people have said they would like to work elsewhere in the EU, when asked if they have a firm intention', the figure drops appreciably."

Mr Kulinicz makes the point that in the case of Britain, there have never been special restrictions on Poles entering the country and there has never been a history of people-smuggling from Poland. He acknowledges that there are already large numbers of Poles working illegally in the UK and his concern is that they may not join the registration scheme.

"Registration will be helpful for everyone," he says. "It will allow people to legalise their situation. It is hoped people are not put off registering themselves."

The reality is that for those working in the black economy, registration may hold few attractions. Gangmasters, like the one operating Andrzej and his friends in Birmingham, are unlikely to want to comply with the niceties of the European Work Directive and the minimum wage.

And for those Poles who have been working legally in Britain, EU accession will make little difference. Piotr, a 35-year-old consultant anaesthetist, has made frequent working visits to the UK. He is planning another trip in April.

"I'm going to work as a locum in an NHS hospital for four weeks," he says. "I need a new car and after a month in Britain I can get a nice Volkswagen Passat estate."

He is taking unpaid holiday from his job in a Warsaw general hospital and expects to work a 70-hour week in Britain. He will be paid £30 an hour, he said, and income tax is taken from his salary at source. He hopes to come home with about £5,000.

In Warsaw, this is fabulous money. A fully qualified hospital doctor earns a basic gross salary of around £600 a month and even with overtime, cannot earn anything like salaries paid in Britain.

"A lot of my friends are doing the same thing," Piotr says. "We are made very welcome in Britain."

Piotr, who is married with two daughters, is not bothering to wait for the accession date before travelling to the UK. In the past, when he needed to extend his visa, he simply popped over to France for the day and re-entered. The alternative, he says, is to spend a day queueing at an immigration office.

They may come from different ends of the employment spectrum, but Piotr the anaesthetist and Marcin the carpenter have one thing in common when it comes to working in Britain - Poland's entry to the EU will change little. According to Marcin, there is an inescapable logic in the situation: "If we are there," he says, "it's because you need us."