Five people may be prosecuted over antisemitism linked to the Labour Party, Britain’s most senior police officer has revealed.

Dame Cressida Dick, the commissioner of the Metropolitan Police, said the force had arrested six people last year as part of its inquiry and that five files have been passed on to prosecutors.

“It is for the Crown Prosecution Service (CPS) to decide,” she told LBC radio.

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“It is a very complex crime type, to be honest – there is a lot for them to look at and a lot for them to consider as to whether there is either sufficient evidence to charge and whether it is in the public interest so to do.”

The investigation was prompted by an internal Labour dossier detailing antisemitic messages on social media allegedly posted by members, which was obtained by the radio station last year.

Reports at the time suggested the documents included details of 45 cases, including one which allegedly read: “We shall rid the Jews who are a cancer on us all.”

The Labour Party has previously welcomed the police investigation and said: “Antisemitism has no place in our society and we are committed to challenging and campaigning against it in all its forms.”

A senior Labour spokesperson said it was believed that all of those referred to by Dame Cressida had either been expelled from the party or left while under suspension. The spokesperson added: “Obviously, all cases of hate crime should be investigated and if necessary prosecuted.”

Reported antisemitic incidents have been rising in the UK amid an overall rise in hate crimes motivated by all factors including race, religion, disability and sexual orientation.

Dame Cressida’s announcement came after The Independent revealed that the proportion of reported hate crimes being prosecuted has plummeted from a quarter to less than one in 10 in the past six years.

Despite attacks reported to police more than doubling to a record of 103,400 in the same period, the number of suspects charged has been steadily falling to just 9,500 in 2018-19, according to an analysis of Home Office and CPS figures.

Prosecutors blame the drop on police, who have been referring fewer cases to be considered for charges.

But the CPS also introduced an 85 per cent target for hate crime convictions in 2013-14.

Like other “levels of ambition”, it was not publicised by the CPS and critics argue the targets may have influenced behaviour by both police and prosecutors.

Reports of hate crime have surged in recent years, hitting peaks during the 2016 EU referendum, the 2017 London and Manchester terrorist attacks and debates about Brexit in parliament.

Additional reporting by PA