Immigration figures: Councils vs the ONS

17 February 2010

Immigration was back in the news today, as a group of councils disputed offical figures regarding the effect of immigration on local population levels.

Yesterday, the FT reported warnings by three councils, Peterborough, Slough and Boston, that government claims of Eastern European migrants returning to their home countries had not been borne out by experiences on the ground.

Representatives of all these councils insisted that the number of new migrants - and hence total population levels - were greater than those suggested by figures from the Office of National Statistics (ONS).

The warnings were picked up by several other news outlets today, including the Telegraph, Mail and Express. This coverage includes specific figures on the possible level of divergence between ONS numbers and carried out by councils.

Boston claims there are 75,000 people living there, compared to the official estimate of 62,000 while Peterborough officials say there are 184,000 not 164,000 and Slough claims it has up to 140,000 people rather than the official 124,000.

The additional demand for public services, and ensuing stretch on local government funding based on population, means it is worth investigating the background to the divergence.

Both estimates work from the 2001 data factoring births, marriages and deaths, along with net migration.  The difference however is between a 'top-down' and a 'down-up' approach.

While migration as calculated by the estimates quoted in the press are derived from on the ground anecdotal evidence and local national insurance figures, the ONS works down from the International Passenger Survey data.

When contacted, Peterborough Council  insisted there was no evidence to suggest a decline in migrants coming to the area and stood by the figures in the press.

A spokesperson told Full Fact that annual National Insurance registrations by foreign migrants had remained broadly consistent at around 4,800 over the past few years.

Taking this as a basis for inflow, the spokesperson said the council had anecdotal evidence to suggest that outflows were not counteracting this.

Link Centres run by the council are attended by a proportion of new arrivals, it was claimed that through such centres the council was able to "get a feel for how many are going back" .

Registration records for children starting school in the area, also backed up the idea that more migrants stayed in the area than official figures suggested.

So what of the official figures?  The guidance issued by the ONS admits that their method, while accurate for calculating national migration, could lead to some uncertainty or inaccuracy at local level. Nevertheless the ONS insist their figures "the best that are available on a nationally consistent basis."

It seems that neither method is perfect, and indeed the ONS is currently conducting research to find if population estimate methods can be improved.

Until then, as Full Fact has previously argued, the divergence in figures serves as warning that most coverage of immigration figures will be at best imperfect.

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