The Accession State Worker Registration Scheme was a temporary measure used in the period from 2004 to 2011 by the UK to restrict incoming workers from the eight member states of the European Union in Central Europe and the Baltic region of northern Europe (the "A8 countries").
Workers from the above countries were required to register on the WRS scheme within a month of joining a new employer.
Those who could not prove that they had registered on the scheme were unable to count any time prior to May 2011 towards the minimum five year qualifying period of residence in the UK, and so could not become eligible to apply for British citizenship until 2016 at the earliest.
If the worker was able to prove that they had worked legally for at least a 12-month period (without a break in employment of more than 30 days) then they gained the ability to claim social security benefits such as Jobseeker's Allowance.
By the time the A8 countries had been in the EU for over seven years (1 May 2004 to 20 April 2011) and the maximum extent of the temporary measures, which were allowed by the Treaty of Accession to the EU (from 2003), had been reached and therefore since then their nationals enjoy the same rights as those of the older member states.