Senior ministers urged the then-Prime Minister Tony Blair to delay granting employment rights to eastern and central European workers when the EU expanded in 2004, newly released files have revealed.

In February that year, Foreign Secretary Jack Straw pointed out that Britain was alone amongst the bigger EU members in offering a “concession”.

The concession meant people from Poland and other newly joined EU countries would be able to work in Britain after 1 May.

Almost all the other large states would not allow this for two years: only Italy was undecided. Smaller EU countries, aside from Ireland, had work permit schemes which would limit numbers.

Papers from the National Archives – which have been released now they are 20 years old – show Straw proposed a six-month delay for the UK.

He said: “I believe we could be faced with a very difficult situation in early May”.

He warned the UK could “be forced to revoke the concession in the least propitious of circumstances”.

His letter was copied to other senior ministers, and the then-deputy prime minister John Prescott supported Straw.

Prescott wrote that he was “extremely concerned” about the potential impact on social housing.

He was also worried that many workers would come to London and the South East, and unable to find decent housing would “resort to sharing overcrowded housing in poor conditions”.

But David Blunkett, the then-home secretary, argued the economy needed the “flexibility and productivity” these new workers could provide.

Eight eastern and central European countries joined the EU in 2004, including Poland. According to the government, the number of Polish nationals living in the UK increased from around 69,000 to around 853,000 over the next decade.

Blair asked whether the UK could have work permits, but instead the Home Office speedily drew up a “workers registration scheme”.

That scheme required A8 workers – those from the eight new member states – to pay a fee and register their employment in a specific job. Failing to do so would incur a significant fine.

From May 2004 onwards, No 10 monitored these registration numbers week by week.

The government was particularly worried because it had publicly estimated that only 13,000 new workers a year would come to Britain after the EU expanded.

The files show that Kate Gross, one of the private secretaries at No 10, wrote to the prime minister on 2 July 2004.

She enclosed a briefing note for the press which would say “the influx of new arrivals predicted by the media simply hasn’t arrived”, even though that 13,000 had been exceeded.

She explained that while 24,000 people had registered with the scheme, most had been living in the UK before 1 May.

Kate Gross’s memo notes that most were young, aged 18-34 – and there was no evidence of them “exploiting the benefits system”. Blair scrawled “that is the key” by the side of that statement.

However Kate Gross noted “the key elephant trap is how these figures relate to previous HO [Home Office] projections”.

If applications continued to increase, she wrote, the number of new arrivals would hit “50-60,000 by May 2005”.

The next set of figures for the scheme showed a drop, and a briefing paper to No 10 said: “It looks like we are over the peak in applications.”

The Immigration and Nationality Directorate “should be congratulated on implementing the workers registration scheme in short order”, it said.

The problem was, the scheme wasn’t providing an accurate record.

The self-employed did not have to register, for example, which excluded many building workers like carpenters.

And there was little enforcement.

The shortcomings of the workers registration scheme were exposed in late 2005, when according to the WRS there were only 95 Polish plumbers in the whole of the UK.

In 24 hours the Daily Mail found 95 Polish plumbers in London alone.

Over the next few years hundreds of thousands of A8 nationals, mostly Polish, moved to the UK.

Though many have now returned, the 2021 census reported 743,000 Polish-born people resident in Britain.