Police have shelved an investigation into antisemitic abuse sent to a former Unite union leadership challenger after admitting they failed to gather the evidence from Twitter in sufficient time.

Gerard Coyne – who narrowly lost out to Len McCluskey in the Unite ballot in March – told the JC he was “deeply concerned” after being notified by police they were unable to proceed with their probe because the social media network did not keep material for longer than 30 days from accounts that had been deactivated by users.

After giving an interview to the JC in the run-up to the Unite election, Mr Coyne alleges he was targeted in a social media smear campaign accusing him of having the “backing” of an alleged “Jewish mafia” along with other classical antisemitic tropes.

Police launched an investigation and interviewed Mr Coyne in March. Officers looked at an account set up under the pseudonym of @1UnionBloke.

But the JC has now learned police officers have contacted Mr Coyne to confirm they could not proceed with the probe as the  account was “deactivated” shortly after it had emerged the complaint had been made.

A police source said: “As the account is now deactivated, Twitter have not got any records of the account, so therefore cannot provide us with any further information to progress our enquiries.

“This means that at this time the crime will be filed pending any further information. We appear to be having these problems with social media at the moment and unfortunately people are aware of this so therefore know that deactivating the account will 'protect' them.”

Mr Coyne said: “It is deeply concerning that data has been deleted and that the perpetrator of this antisemitic abuse has got away.”

Among of series of anti-Jewish messages sent from the account was one featuring a superimposed photo of Mr Coyne’s face on an image of a Jewish man brandishing a gun, with the wording: “Be warned @gerard_coyne has backing now!!”, along with the phrase “Jewish Mafia”.

Other messages from the account, all of which attempted to promote support for Mr McCluskey’s campaign, included suggestions Mr Coyne was pandering to the Jewish community in his leadership campaign.

Following his defeat to Mr McCluskey in the Unite ballot by just 6,000 votes, Mr Coyne was controversially sacked as West Midlands regional organiser over claims he had misused data.

The union election was described as a battle for the heart and soul of the Labour Party, which Unite bankrolls with £1.5m a year. 

The Unite investigation into Mr Coyne was led by Andrew Murray, the union’s chief of staff who was seconded to Jeremy Corbyn’s campaign during the general election.