Border guards at Heathrow Airport have been privately told not to ‘waste time’ interrogating potential illegal immigrants, and instead focus on jihadis with European travel papers.

Terrorists must be the Border Force’s “number one” priority, according to a leaked memo seen by the Mail on Sunday, because extremists entering Britain with European Union (EU) documents don’t require visas.

The memo comes as thousands of EU citizens who fought with ISIS are fleeing Iraq and Syria, attempting to return to Europe as the Islamist terror group loses ground.

Warning Islamists are plotting “indiscriminate attacks on innocent civilians” in UK cities, in February Britain’s terrorism watchdog Max Hill expressed “enormous concern” at the prospect of large numbers of returning jihadis.

Deputy director of Heathrow Airport’s Border Security Command, Nick Jariwalla, spelled out the threat in a recent message to Border Force guards entitled “Protecting the Public”.

In it, he insisted staff change the way they work so as to “really focus” on the threat of terrorists arriving from Europe, writing: “We are not sufficiently focused on the threat from passengers seeking to enter on EU documents.

“This is the number one thing that colleagues from the security services talk to me about.”

Interrogating potential illegal immigrants is “a poor use of our time”, Jariwalla told staff in the memo, stating that visa holders already have permission to enter Britain.

“We must recognise that every minute you spend with a potential doubtful visitor is a minute less you have to spend on passengers who might have more sinister intent,” he added.

A Home Office representative told the Mail on Sunday: “100 per cent of scheduled passengers are checked when arriving in the UK’ and visa holders are subject to ‘extensive mandatory checks.”

Earlier this year Breitbart London reported that illegal migrants found stowed away in lorries are frequently told to make their own way to a processing centre more than 50 miles away, and that Britain’s lax border controls mean authorities have “no way of knowing” the identities of individuals entering the UK.