The Office for National Statistics has been told to launch an urgent review of Britain’s official immigration figures ahead of the European Union referendum amid concerns they may be wrong, The Telegraph can disclose.

In a development which will intensify public debate about immigration ahead of the June 23 vote, the UK Statistics Authority (UKSA) has written to the head of the ONS pointing out “speculation about the quality” of migration figures.

The watchdog said the public must be told if official immigration data “falls short of providing a full picture”.

Campaigners described the watchdog’s letter as “extraordinary”.

The letter revealed the UKSA’s concerns focus on differences between ONS migration figures and data produced by other government departments - which have shown a discrepancy of more than a million EU migrants over the last five years.