Less tangibly, some employers say in a barely audible whisper, immigration has given relief from demanding Irish youngsters who have absurdly high expectations . . . and too often appear to be planning their next move before they have even put their noses to the grindstone. This is very different from their newlyarrived eastern European counterparts, who are keener than mustard to muck in and seem refreshingly grateful for the opportunity to toil.

The story across the water in Britain is similar.

Although the arrival of eager European youths has been only a fraction of the influx into Ireland in proportional terms, the benefits to employers have been broadly similar.

It seems curious, then, that Ibec's UK equivalent, the Confederation of British Industry, recently suggested a "pause" in immigration. Does this make sense, and should Irish employers pay heed to the call?

The trigger for British business's intervention was the imminent decision on whether to extend to Bulgarians and Romanians the freedom to work in the UK once the two aspiring members of the EU join sometime over the next 18 months. (Governments in the 25 member states are to give the pair a hard accession date in October. ) The CBI says that the net economic gains to the British economy of recent immigration are big, which no serious analyst contests, but that the costs in the future may outweigh the gains, particularly if the jobs market doesn't soak up a second big inflow.

At this point, some context is necessary. Open debate about immigration is fraught because there is a real danger of giving those with xenophobic tendencies hard facts to support their prejudices. This would be reason enough not to raise the matter if the risks and potential costs associated with immigration were small. Unfortunately they are not.

A careful balance in the discussion is needed so that the serious consequences and implications can be explored without fuelling reactionary sentiment by, for instance, railing against "job displacement" and "wage degradation" on the basis of evidence that is anything but solid.

There are multiple aspects to the immigration question, and this column intends to tackle some on an occasional basis in the future, but space permits discussion of just two today.

The first is the impact of inflows of workers on the position of the Irish economy on the value chain. Some straightforward economics is needed to do this. The three basic inputs to any business are land, labour and capital, which economists call the "factors of production". Business decides what mix of these to use in their operations depending on the price of each relative to the others.

An increase in the supply of cheap labour tends to cause a fall in its relative price. This makes businesses more inclined to take on extra workers and less inclined to spend on plant and machinery. If this happens (and, it must be stressed, there is no evidence that it has in Ireland) it would logically make the average Irish company more labour intensive and less capital intensive.

As people's wealth in an economy ultimately depends on the amount of capital each person employed has to work with, any development that causes the stock of capital to grow less strongly is not necessarily a good thing.

Indeed, in today's global economy it is probably bad . . . not least because it would increase exposure to labour-intensive economies such as China, which is ultra-competitive.

The second issue worth pondering is the costs associated with immigration. Again, considering the matter from a "factors of production" perspective is helpful.

While the free movement of these factors is generally good, it can have damaging consequences. This was to be seen in the 1990s, for example, when large amounts of capital flooded into many emerging markets, creating unsustainable booms.

Crises in Mexico, across Asia and in Russia between 1995 and 1998 caused a major rethink among economists about the downsides of freely moving capital.

In the case of labour movements, there is a theoretical point where the costs of immigration in terms of congestion, strains on social services and higher property price inflation offset the many gains. But because many of these costs are not measured in Ireland, it is impossible to identify this point.

It would seem prudent for the government to engage in more data collection on these costs because the accession of Bulgaria and Romania has the potential to increase immigration considerably.

What sort of numbers could be involved?

Although it is impossible to predict accurately, the combined population of the two countries is 30 million, which compares with 75 million in the 10 member states who joined in 2004.

The absolute potential for inflows is, therefore, smaller.

However, the attraction of relocating is considerably greater among these 30 million people than their 75 million neighbours already in the EU because income differentials are much greater. GDP per head in 2004 was US$3,100 in Bulgaria and US$3,385 in Romania, but over US$9,000 in the 10 previous accession states.

The rapid multiethnicisation of Ireland has unsettled many who are averse to change, and politicians of all hues warn privately that the passive disgruntlement people are expressing on the doorstep could become more active and a lot nastier if the spectre of joblessness were to return.

But it may not even take such an unpleasant occurrence for nastiness to rear its head, as has been demonstrated in the Netherlands recently independently of economic developments. Although it would be wrong to extend the parallel too far (Poles are reCatholicising Ireland, while Muslim immigrants are Islamising parts of the Netherlands), it would be unwise to assume that social tensions could not come to the fore in Ireland.

Business needs to be mindful of a backlash. If anti-immigration sentiment were to rise and become more focused on individual immigrants, that would be bad for everyone . . . not least human resources departments trying to manage workplaces that are already very mixed.

Dan O'Brien is a senior editor at the Economist Intelligence Unit.

danobrien@economist. com