The Labour lost members at a rate of 125 a day last year as allegations of antisemitism continue to dog the party.
Annual accounts published on Thursday revealed the membership fell by 45,784 from the end of 2017 to the end of 2018.
Labour had 564,443 members in 2017 – thanks to the massive influx of supporters who joined to support Jeremy Corbyn – but that number had fallen to 518,659 by 31 December 2018.
The Times reported party insiders believe that the real membership is now around 450,000, after ‘lapsed’ members — those who have simply not paid to renew their subscription — are taken into account.