This week Full Fact – a fact-checking organisation now regularly heard on the BBC – attempted to check the following claim put to Ed Miliband by Jeremy Paxman during the leaders’ interviews of 26th March 2015:
“You were predicting figures of between 5,000 and 13,000 immigrants a year from the expansion of the EU in 2004 and actually something like 400,000 people came in.” 
Mr Paxman was referring to the government commissioned report, authored by Professor Christian Dustmann et al which estimated that between 5,000 and 13,000 migrants from the A8 countries would come to the UK following their accession in 2004.  The estimate was used to reassure the public ahead of the accession and to justify the decision not to impose transitional controls on workers from the new EU countries.
At the time Migration Watch UK called this estimate ‘almost worthless’ and we were correct. See here.
The official migration statistics for the decade following accession estimated that net migration averaged almost 50,000 per year. However, the Census of 2011 revealed a significant undercount. An ONS review of the net migration statistics suggested that they had undercounted net migration by around 350,000 across the decade, principally from Eastern Europe between 2004 and 2008. This suggests an additional 50,000 a year bringing the total to some 100,000 East European net migrants a year. Migration Watch UK have called on the ONS to revise the migration figures but they have so far failed to do so. On the other hand, the ONS has carried out census-based adjustments to the official labour market statistics which show that by the end of 2014, the number of A8 workers in the UK had increased by nearly 850,000 (i.e. not including dependent adults or children). Meanwhile, the Annual Population Survey shows that the A8 population has increased by over 900,000 in the ten years from 2004 to 2013 – also suggesting net migration of just under 100,000 per year. While these are different data sets they provide a consistent pointer as to the scale of net migration over the last decade.
The Full Fact article ‘Faulty figures or misinterpretation? EU migration predictions under Labour’ offered Professor Dustmann the opportunity to clarify his prediction of between 5,000 and 13,000 migrants a year. According to the article Professor Dustmann was commissioned to provide an estimate on the assumption that all EU countries opened up their labour markets to A8 workers. Of course only the UK, Ireland and Sweden did so with every other government opting to impose transitional controls.
Full Fact reports that Professor Dustmann claims that he predicted that 46,000 would come to the UK if other countries kept their labour markets closed. However there was no such number in the report, its Executive Summary stating:
“In the case that Germany restricts free movement of workers for a longer period than the UK, some of those immigrants to Germany may use the UK as a destination. However, even in the worst case scenario, migration to the UK as a result of Eastern enlargement of the EU is not likely to be overly large.”
While Professor Dustmann has pointed out elsewhere that his report suggested that up to a third of potential migrants to Germany might come to the UK instead if Germany imposed transitional controls, he also makes clear that "this was a speculative observation rather than an estimate". 
So it not true that Professor Dustmann had estimated that migration would be around 46,000 a year. His actual estimate, rather than any speculative observation, was in fact out by a factor of 10, taking his median prediction. It was clear that the estimate at the time was likely to be incorrect and, indeed, we said so in clear terms at the time.
Full Fact are establishing themselves as a leading independent fact checking organisation and so it is all the more important that they stick to the facts. The fact here is that Professor Dustmann's subsequent self-justification cannot alter that his estimate – widely reported as an authoritative indication of likely Eastern European migration to the UK – turned out to be simply wrong.
 Jeremy Paxman, ‘Cameron and Miliband: The Battle for Number 10’, Channel 4/Sky News, 26th March 2015.
 Dustmann, C., et al, The impact of EU enlargement on migration flows’, Home Office Online Report 25/03, page 8, URL: http://discovery.ucl.ac.uk/14332/1/14332.pdf
 Christian Dustmann and Ian Preston, ‘How Early Estimates for Migration Flows after EU Enlargement in 2004 are Misinterpreted’, CReAM Blog, 16 January 2014, URL: http://creamcomments.blogspot.ie/2014/01/how-eearly-estimates-for-migration.html