On 28 July 2013 British Members of Parliament published a report on the statistics on migration to and from the UK. The Commons Public Administration Select Committee (PASC) says in the report that migration statistics produced by the Office for National Statistics (ONS) and the Home Office are blunt instruments for measuring, managing, and understanding migration in the UK and that a full and accurate account of migration to and from UK would be needed, which of course requires new sources of statistics.

PASC says the current instruments are not accurate enough to measure the effect of migration on population, particularly in local areas, nor the social and economic impacts of migration. "Current sources of migration statistics were established at a time when levels of migration were much lower than they are today. These sources are not adequate for understanding the scale and complexity of modern migration flows, despite attempts to improve their accuracy and usefulness in recent years.", the report says.

In the first half of 2012, immigration was estimated at 515,000 persons. Around 30% of this was by nationals of other EU countries, and around 55% was by non-EU nationals. Emigration was estimated at 352,000, of which 44% were British nationals, around 24% were nationals of other EU countries, and around 32% was by non-EU nationals. Net migration, the difference between immigration and emigration, was estimated at 163,000.

Annual estimates of immigration are primarily based on a sample of around 5,000 persons identified through the International Passenger Survey, which is a survey of people travelling through UK air and sea ports. These estimates are subject to a large margin of error.

According to the British report, the Government aims “to reduce net migration from the hundreds of thousands back down to the tens of thousands” by the end of the current Parliament, which means a ten fold reduction in net migration. In practice it only needs to be roughly halved in order for the Government to achieve its aim. "Clearly these statistics are not fit for purpose in the longer term. There is also the problem that few people understand what 'net migration' is. It tells you nothing about how the nature of the UK population is changing, because the total immigration figure is partly offset by large numbers of UK nationals leaving.", said Bernard Jenkin, Chair of PASC. Although some aspects of official migration statistics could be considerably improved if the Home Office and ONS properly recorded and linked the data they already gather, according to the British Parliament report, new sources of migration statistics still need to be developed.

Source: http://www.parliament.uk/business/committees/committees-a-z/commons-select/public-administration-select-committee/news/migration-statistics-report-published/