British citizens living overseas are currently entitled to be registered to vote in UK Parliamentary elections. These are known as "overseas voters". These overseas voters must register in the constituency in which they were registered before leaving the UK and currently registration must be renewed annually for up to 15 years after leaving. People who left more than 15 years ago are ineligible to register.
The Elections Act 2022 will change this position. The Act received its Royal Assent on 28 April 2022 and includes provisions to removing the 15-year rule. The change was supported by the Liberal Democrats in parliament and was included in the Party's 2017 and 2019 manifestos.
Detailed secondary legislation is required to implement many aspects of the new provisions. It is expected this legislation will be brought forward in 2023 with newly eligible overseas voters eligible to vote in 2024. It is currently expected that about 3.5 million UK citizens living abroad will be entitled to vote.
A Commons Library Briefing is available at https://researchbriefings.files.parliament.uk/documents/SN05923/SN05923.pdf for more information.