LABOUR has screened up to 40,000 calls to trade unionists to stop a supposed far-left infiltration into the party leadership race.

Interim leader Harriet Harman revealed yesterday that the party is “listening in to phone calls” to vet new supporters.

And a party spokesman told the Morning Star that she was making reference to the monitoring of calls made by general union Unite.

Ms Harman added that she is “absolutely determined” that new rules opening up the leadership election were not “exploited” by supporters of other parties. 

The spokesman claimed that Labour have so far uncovered and blocked thousands of applications.

They include one person who said they wanted to register as a supporter “to bring about the destruction of the Labour Party.”

The Labour spokesman said: “While we want the widest number of supporters to have their say in Labour’s leadership contest, the Labour Party has a robust system to prevent fraudulent or malicious applications.”

All political levy-paying members of affiliated unions automatically had a vote in the last leadership election, but unions now have to sign them up as supporters if they are not already party members.

When affiliated unions sign-up a supporter they are required by Labour to provide their name, email address and telephone number.

The information is checked by Labour centrally and at a local level to ensure they are not well-known members of rival parties.

Unite has launched its own campaign to contact members by phone to sign them up, meaning they have to record the conversation and send the tapes to Labour.

Two-thirds of all the conversations, most of which last around five minutes, are listened to by Labour staff.

So far the union has submitted between 30,000 and 40,000 conversations to be checked.

The exhaustive task is being carried out by a 48-strong call centre team based in Newcastle. No new staff have been taken on to carry out the checks.

A Unite spokesman said: “The process of verification is a matter for the Labour Party.”