Labour officials have been identifying up to 1,000 suspected “entryists” a day as they try to stop members of rival parties and hard-left factions influencing the party leadership contest.
Staff are trawling through the social media accounts of 180,000 “registered supporters” who have paid £25 to vote, a majority of whom are believed to back Jeremy Corbyn.
The scale of the operation has been revealed after Tom Watson, the deputy leader, provoked a bitter row with Corbyn when he raised concerns about “Trotskyist entryists” last week.
Labour leadership: Members drop voting legal challenge
Labour members have abandoned a legal challenge against rules which will stop new members voting in the party’s leadership contest.
On Friday the Court of Appeal ruled Labour was within its rights to stop some new members voting in the contest between Jeremy Corbyn and Owen Smith.
It overturned an earlier High Court ruling that the ban was unlawful.