The UK Independence Party has added a clock to its website to count down the days until 1 January 2014, when controls expire on immigration from Romania and Bulgaria, the two newest EU member states. It is a shameless piece of scaremongering designed to support Ukip's alarmist claim that the change will result in an influx of 350,000 Romanian or Bulgarian migrants to the UK. Today the lobby group MigrationWatch plucked from the air another dubious figure, saying there will be around 50,000 new arrivals every year once restrictions are lifted. It predicted "significant consequences" for housing, jobs, schools and hospitals.

The justification for this moral panic is the fact that the Government got the figures so wrong last time around. When Poland joined the EU, the Home Office infamously predicted that no more than 13,000 Poles would come to Britain annually. Within two years 264,560 had arrived. Things are bound to be even worse this time, the prophets of doom suggest, because the minimum wage in Romania and Bulgaria is half that in Poland. Low-skilled immigrants will flood in to undercut British workers.

Such is the myth. The real impact, according to the Migration Observatory at Oxford University, will be far smaller. There are many reasons to suppose they are right. When Poland and others joined the EU, the UK was the only large member-state to open its labour market; in 2014, by contrast, all major European economies are lifting controls. Most Romanians, for instance, are expected to go to Italy, Spain and France, with which they have linguistic and cultural links, and where many already have relatives. Those deterred by the high rate of youth unemployment in those countries are more likely to head for Germany and the Netherlands than Britain. Plus Bulgarians and Romanians generally have a weaker command of English than Poles.

In any case, contrary to popular scare stories, immigration is, on balance, good for the British economy. Many immigrants have made huge contributions to our society. Migrants create jobs as well as competing for them. Immigrants often have a particular dynamism. They often do jobs that local people on benefits will not do. They perform vital tasks in the public services. They are generally young, and have more children, which is good news, given the ageing population. Businesses report they have a strong work ethic. The economy grows faster because of their contribution.

All of that is lost on the myth-peddlers who suggest immigrants are all on benefits – when 97 per cent of registered migrant workers have full-time jobs – or more prone to crime, when the Association of Chief Police Officers says offending rates among Polish, Slovak, Lithuanian, Romanian and Bulgarian incomers are pretty much in line with the rest of the population. So critics resort to smears, confusing Romanians with Roma, or planting other dog-whistle racist innuendos – of which, it must be feared, we will hear more when the Australian spin-doctor, Lynton Crosby, masterminds the next Conservative election campaign.

If the net effect of migration is positive, however, there will always be some who lose out. Politicians, national and local, need to focus on criteria for social housing to quash any suspicion that migrants can jump the queue. Extra support needs to be given to schools and hospitals in areas with large numbers of newcomers, and eligibility for benefits should require a minimum period of residency, with offspring who live abroad not eligible for child benefit. But all that can be done within a context of celebrating the virtues of immigration. Demonising new arrivals is not a useful response.