Net EU migration into the UK has been underestimated by as much as 16 per cent by Britain’s official statisticians.

The Office for National Statistics (ONS) said the error meant there were almost 30,000 more migrants from the EU8 countries which include Poland over a year than it had previously estimated.

By contrast, the ONS said it had over-estimated net migration from outside the EU by around 13 per cent. That meant it was around 25,000 lower in a year than previously estimated.

As a result, the status of the quarterly immigration figures, which are due to be published on Thursday, have been downgraded to “experimental statistics.”

The estimates have been based on the International Passenger Survey, which critics say is unreliable as a measure of true levels of migration.

The ONS said it was moving to a more robust system based on Government data including the tax returns of migrants, health and education data, which should provide a more accurate picture of migration trends.