There will be no flood of Bulgarians and Romanians. But in any case, wasn't it the Tories who championed a 'wider' Europe?

David Cameron's sudden crackdownon EU "benefit tourism" six weeks before Romanians and Bulgarians get unrestricted access to the British and European labour markets is a sad reflection of ministers' failure to tackle increasing fears that have been voiced all year over their arrival.

Only last week, in the face of an incipient Tory backbench rebellion, the immigration minister, Mark Harper, finally set out the official assessment of what is likely to happen in the new year and why it is unlikely to be a repeat of 2004, when Poles and other eastern Europeans were allowed to come and work in Britain.

It is worth remembering that Romania and Bulgaria actually joined the European Union in 2007 under accession treaties voted for by the Conservatives – who were always the party most enthusiastic for a wider rather than a "deeper" Europe.

The treaties provided for a seven-year transition period, after which Romanians and Bulgarians would be free to work anywhere in the European Union, including Britain. That day will arrive on January 1.

As Harper told the potential Tory rebels last week, any move to extend those restrictions any further by Britain would immediately be ruled illegal under the accession treaties. No European court need even hear the case: the high court in London would be more than likely to declare the move illegal.

In the face of some of the more hysterical predictions, such as that all 21 million Romanian citizens will up sticks and come to Britain, the government has wisely avoided trying to predict numbers, arguing that that is a "fool's errand".

But it has set out the reasons why numbers are unlikely to replicate the mass arrival of the Poles 10 years ago.

In the first place, in 2004 Britain was one of only three larger countries, along with Sweden and Ireland, to allow the Poles immediate access to the labour market; this time, eight other countries, including that job-creating powerhouse of the eurozone, Germany, will open their borders at the same time.

In the second place, as Romanian and Bulgarians ministers keep explaining, the big migration of their citizens took place in 2007, when they joined the EU. Then, 3 million Romanians left to live in other parts of the EU.

The vast majority went to live and work in Italy and Spain, in each of which the Romanian and Bulgarian communities number more than 800,000, and where the labour markets have already opened to them. Fewer than 130,000 live in Britain.

This doesn't mean to say, however, that nothing should be done to address anxieties that any new wave of migration may put extra pressure on public services.

Cameron and his home secretary, Theresa May, knew this back in April when they first wrote to the European commission, along with the Germans, Dutch and Austrians, pressing for fresh action to curb so-called benefit tourism. In particular, they pressed then for effective sanctions against EU migrants who abuse freedom of movement or defraud the benefits system. The joint letter admitted that those people could already be expelled under existing EU powers but complained that they could not be barred from re-entering the country virtually the next day.

As neither Romania nor Bulgaria is joining the Schengen EU free movement area on January 1, it may well be open legally to Britain to secure a joint agreement that anybody found begging or sleeping rough be sent back to those countries and then barred from re-entry for 12 months – although that would raisehuman rights concerns.

Given that fewer than 6% of EU migrants in Britain claim out-of-work welfare benefits, including job seeker's allowance, within six months of registration, and an smaller proportion of that number are found to be fraudsters, this is a narrow point.

Jonathan Portes, the former chief economist at the Department of Work and Pensions has said that the changes in the habitual residence test, too, are just tweaks to the system that will affect few migrants.

The commission has repeatedly asked Britain and Germany for hard evidence of the scale of benefit tourism, but it has not used the lack of this as an excuse to do nothing. There have already been moves to tighten access to other welfare benefits, and many other EU countries already require contributions, such as national insurance payments, to be made before migrants can gain access to public services and benefits.

Many of the media and political anxieties centre on the possible arrival of more Roma people but few realise that they make up only 3% of the total population of Romania. The typical Romanian migrant is far more likely to be young with a higher skill profile than other migrants and without – at least initially – a family, thus limiting their potential demand on services.

The Conservatives, especially John Major, championed the cause of the enlargement of the EU partly to counter what they saw as the Europhile drive towards ever deeper integration.

Major travelled the capitals of the former communist states of eastern Europe to persuade them to rejoin Europe, amidmuch talk of a "common European home", rather than be left locked into a former Russian empire. The law now says those people cannot be treated as second-class Europeans any longer.