Net migration to the UK in the year to June 2023 has been revised up from an initial estimate of 740,000 to an estimated record 906,000, while the total for the year to December 2023 has been revised up from 685,000 to 866,000.

Estimates of migration to and from the UK typically undergo a number of revisions as more data becomes available, but the scale of the latest revisions – a jump of 166,000 in the total for the year to June 2023 – reflects recent changes and improvements adopted by the Office for National Statistics (ONS), which publishes the figures.

Long-term international migration refers to people entering or leaving the UK for a period of at least 12 months.

The ONS publishes an initial estimate of net migration before 12 months has passed, but this means it does not have a complete set of travel data and has to make assumptions about how long the new arrivals are likely to stay in the UK.

As time goes on, more information becomes available to show the impact of new arrivals on the population, such as visa applications, higher education statistics and tax registrations.

The ONS is now making greater use of this type of information when calculating revisions to its initial estimates of migration.

For example, a more complete and up-to-date set of travel information has added around 25,000 people to the previously published estimates for the year ending December 2023.

Statisticians now have a greater understanding of the types of visas granted to people who came to the UK under the Ukraine resettlement schemes.

The inclusion of additional Ukraine immigrants has added 43,000 to the immigration total for the year to June 2023 and 30,000 to the total for the year ending December 2023.

The ONS is also drawing on other sources to inform its revisions.

“We now use our knowledge of past migration by age and nationality to improve our assumptions on whether those who have recently arrived in the UK will become long-term migrants,” according to ONS director of population statistics Mary Gregory.

“This should improve our estimates and make them more resilient to any future changes in patterns of behaviour.”

In addition, the ONS has improved the way it identifies people who have come to the UK from outside the EU+ area and who have then moved to a new type of visa – for example, students moving on to graduate visas.

The EU+ area covers all countries in the EU plus Norway, Iceland, Liechtenstein and Switzerland.

“Previously we could only see that an individual had a new visa if they travelled on that visa – this meant if a migrant stayed in the UK without travelling, we would not see their change in visa and would assume they had left the UK when their original visa expired,” Ms Gregory said.

“We can now see when people move to a new visa as soon as it is granted.

“This has reduced non-EU+ emigration, especially student and work dependants. For example, for the year ending December 2023 we have reduced our emigration of non-EU+ nationals by 69,000 from 233,000 to 164,000.

“This increased knowledge and understanding should reduce revisions in future.”