She was one of the first. And now she wants to go home. Agnieszka Siedlaczek came to Scotland before mass migration from Poland began in 2004. She had family to look after here: an elderly "babcia", or granny, who was among the thousands of Poles who made Britain their home after the Second World War. She was warmly welcomed, and has thrived. But she is leaving.

"I miss my home," says the 28-year-old hairdresser and entrepreneur. "I miss my family, my friends; I miss them very much. I want to go back. Scotland is really lovely and life here has been better for us. I am not saying it's not nice. It's just not my country."

Agnieszka, who has built her own successful business in Edinburgh, isn't alone. Around half of the one million workers, mostly young, who came to the UK over the past four years have gone home, according to the most comprehensive study of the migration that followed the expansion of the European Union in May 2004. That, most experts reckon, was always to be expected: many migrants would come to the UK for a year or two to earn some money or learn some English.

Now, however, a new worry is sweeping businesses. What, economists are asking, might happen if there are no new arrivals to replace Agnieszka and others who go home? Scotland is desperately short of labour, skilled or otherwise. It is also, to be blunt, short of people, especially young people.

Most of the new EU arrivals came from Poland and are educated and conscientious workers. Business leaders describe them as indispensable. Does Scotland need the Poles more than the Poles need Scotland?

The omens are not good. A whole range of economic factors are conspiring to make the UK - and Scotland - less attractive to migrants from central and eastern Europe. Staying put is more of an option. Economies to the east are now recovering well following the horrendous shock of the end of communism in the late 1980s and early 1990s, when most of the youngsters coming to Scotland were at primary school.

Poland, for example, is currently posting growth of 7% (a figure that would make Gordon Brown, fighting to stave off recession, salivate). Its wages are rising and unemployment is falling. Its currency, the zloty, isn't doing badly either. When Poles started coming to the UK in 2004 they were getting seven zloty for every pound they earned. Now they are getting four.

Average wages are still much higher in Scotland than in Poland. Nine out of 10 eastern Europeans in the UK, however, earn less than £400 a week; seven out of 10 earn less than £6 an hour. "The money in Scotland is still good," says one migrant. "But it's no longer super-good."

Staying at home isn't the only alternative to coming to Britain. Wannabe migrant workers might also consider Euroland. The UK, along with Ireland and Sweden, opened its doors to the so-called Accession Eight or A8 group of nations in 2004. Other countries, such as France and Germany, kept some restrictions, which are now being gradually loosened. The pound hasn't just dropped against the zloty, it's down against the euro, too - and that might just make other European nations more appealing than Scotland to migrants and seasonal workers from countries such as Poland.

Farmers may be the first to feel the effects of the migrant crunch. They have come to rely on foreigners, often students, to pick crops such as strawberries. Some have come under fire for providing poor accommodation and lousy conditions for their workers. Now they are having to raise their game: a summer in a damp caravan in Angus is not as alluring as it once was for A8 students.

New restrictions on seasonal workers from outside the EU aren't helping. Some farmers are openly worried about how they are going to get their crops in this summer. Anna Davies, communications manager at the National Farmers' Union Scotland, says: "For many years, the Scottish soft fruit and field vegetable sectors have had to depend on non-UK migrant workers. Changes to the way harvest workers are permitted to come into the UK have already had a negative impact on labour availability and this is expected to get worse this year.

"Farmers do go the extra mile to attract workers - some will provide English-speaking classes or tourist excursions for foreign workers at the weekends, as well as paying attractive wages.

"Although overall it may be too early to tell, the fear is that, as last season, the result of the migration changes will be that some farms have insufficient workers to complete their harvest and that, in the worst case, produce is left to rot in fields.

"This would be demoralising for growers who have invested time and money producing a crop to see it go to waste - even more so with production costs rising at rates well above inflation."

Many eastern Europeans have made their way to Scotland's cities, where they now make up around 1% of the population. But it is in rural areas where they have had the biggest impact. IPPR, a London think-tank, has calculated that there are 90 A8 nationals for every 1000 people in Boston, Lincolnshire.

Scotland's farming and tourism heartlands haven't faced quite such an influx. Figures are, nevertheless, impressive. IPPR puts the A8 population in Perth and Kinross at 29 for every 1000 locals, with 21 in Angus, 16 in Highland and 12 in Aberdeenshire and Edinburgh.Small businesses are particularly vulnerable to any exodus of both seasonal tourism workers and permanent skilled labour. They are watching the pound slip against the zloty and euro with concern.

"There's no doubt that the Scottish economy is still beset by huge skill and labour shortages - and it is small businesses that are hardest hit," says Andy Willox, Scottish policy convener at the Federation of Small Businesses.

"The smallest firms, with less than 10 employees, find it hard to fill most of their vacancies and one in two of these vacancies is hard to fill because of skills shortages. In other small companies, skills shortages account for over a third of their hard-to-fill vacancies. Our members therefore rely heavily on migrant labour to fill these gaps and it would be deeply concerning if a pound which was weakening against the euro saw these vital workers relocating home or to elsewhere in Europe.

"Until our domestic labour market catches up with the needs of businesses, it is in our economic interest to continue to encourage workers not only to come to Scotland but to settle here and help build our economy for years to come."

Scotland, of course, still has a special appeal for Poles. The countries have more in common than many, especially in Scotland, realise. Scots traded heavily with the Baltic region before the Union turned attention to England's colonies across the Atlantic. Communities of merchants thrived in Polish ports and cities - Gdansk even has suburbs called Nowe Szkoty and Stare Szkoty, new and old Scots.

Many Poles, of course, settled in Scotland after the last war, perhaps 15,000 all told. Families such as Agnieszka's had real, human connections.

There is one big draw for Poles and other eastern Europeans, notably Slovaks, Lithuanians and Latvians, coming to Scotland, at least for a spell: the English language. Karol Chojnowski, from Edinburgh, explains why. "Most young people learned English at school and many want a chance to improve their skills," the 27-year-old says. "That was my reason for coming. If you speak fluent English, you improve your employability back home. In fact, if you have any experience of working abroad then that shows you are a person to take seriously."

Karol arrived in Scotland nine years ago, as a student, and has no plans to go back to Poland. The reason? "Well, there was a beautiful girl at my college in Kirkcaldy," he says. "We are getting married in September." The pair also worked together part-time, making whisky crates at a Fife factory. Now Karol has his own business, a website portal for Poles in Britain called www.emito.net. A fifth of his site's visitors are in Poland, thinking of coming to Scotland. Will new arrivals dry up?

"I don't think so," he says. "There will always be a rotation. Some will go; others will come. True, there has been a slowdown in that rotation."

Are there other reasons why Poles might go home? The IPPR found that homesickness was widespread among returning migrant workers. Most central Europeans who come to Scotland like the country. Some revel in its liberal values. Others, however, aren't so sure.

One Balkan migrant told The Herald, on condition of anonymity, that many of his fellow countrymen and women were happy to spend a year or two in Scotland but they certainly wouldn't want to bring up their children here. "The weather is awful," he said. "And is getting drunk and vomiting in the street really the only way to have a good time?"

Children are crucial. Scotland's population has bucked forecasts of decline, partly because of the babies being born to migrant mothers. Some of those mums or would-be mums, however, are thinking of home. Agnieszka is about to get married to a fellow Pole currently working as a builder in Scotland, Klaudiusz Jasinski. (Ironically, Poland is now short of construction workers for major projects such as the stadiums needed for the 2012 European football championships, which the country is co-hosting).

They are going home to her native province in southern Poland, where they are building one of the area's handsome detached wooden homes. But Agnieszka isn't cutting her ties to Scotland altogether. She will keep her hairdressing business, Smartcut, on Edinburgh's Easter Road - and will open one up in Poland, too.

"We will leave next year," Agnieszka says. "We are just two and a half hours from the Tatra mountains and it is really beautiful. Things are getting better there, I hear."

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