The Labour Party’s accounts and this membership facts are available on the Electoral Commission site.
On membership, they say, “As at 31 December 2025 the total individual membership of the Party was 264,754 (2024: 333,235).” That’s a 21% decline on the year and over 50% from when Starmer took over.
For more, see the Data file, in .xls.
Labour’s Membership 2025