Concerns about the quality of official migration figures have been raised by the statistics watchdog.
The UK Statistics Authority (UKSA) has warned that discrepancies between different sets of figures "could undermine public confidence" in the data.
With the next set of figures due in May likely to feature prominently in the EU referendum debate, the UKSA said that any shortcomings in the data must be made clear.
The UKSA's concerns are disclosed in a letter from its head of regulation Ed Humpherson to the Office for National Statistics (ONS) posted on the UKSA website.
In it he draws attention to the differences between the ONS's international migration estimates and Department for Work and Pensions (DWP) figures for National Insurance numbers issued to foreign nationals (NINO) which are traditionally higher.
"The lack of a clear understanding and explanation of the differences between the DWP and ONS figures has led to speculation about the quality of these National Statistics," he said.
"There is a significant risk that a lack of progress in reconciling and explaining the differences over the coming weeks could undermine public confidence in official migration estimates."
Mr Humpherson said the NINO figures were currently being assessed by the UKSA for compliance against its code of practice and he questioned whether they should continue to be included in the official figures.
"It seems clear to me that the issues we have identified to date, including those of coherence with other sources noted in this letter, are relevant factors in considering whether the NINO statistics meet the highest standards of trustworthiness, quality and value, and hence their National Statistics status," he wrote.
He added: "The ONS's May publication will form part of the statistical evidence informing public debate on immigration levels ahead of the EU referendum on 23 June.
"Should it become apparent that this publication will fall short of meeting any expectations that it will provide a full picture of the differences between migration sources ... I would expect ONS to make this known publicly as soon as possible."