Secret code word England fans should yell if they feel in danger ahead of Euro 2024 opener as 500 Serbian hooligans expected to be 'shipped in'

Staff at games, upon the mention of PANAMA, have been told to "immediately offer the possibility of a place to retreat" for anyone who speaks up.

Any under-threat supporters can expect a "multilingual, multi-professional team which is trained in crisis intervention, non-violent communication and de-escalation" to step in and cool things down.

Around 40,000 English fans are expected to arrive in Germany this week for their first group-stage game against Serbia - compared to just 8,000 from their early tournament opposition.

But the match has already been designated a 'high risk' tie by tournament organisers Uefa owing to concerns over fan trouble - a stark reminder of the chaos on the streets of Marseille at Euro 2016.

The chief of police in Gelsenkirchen - the stage for England's curtain-raiser - Peter Both, has raised concerns that a hundreds-strong hooligan horde is expected to arrive in Germany.

"Up to 400 or 500 ­violence-seeking ­Serbian ­hooligans will travel to ­Germany, but we don’t know it exactly and so that's our problem at the moment," he told the Guardian.

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Both continued: "I guess the biggest challenge for us will be to identify violent, disruptive groups at an early stage, to separate them from peaceful and law-abiding fans - that will be our biggest challenge."

While the police chief added that there had been "brilliant" cooperation with British authorities - over 2,000 troublemakers have already been handed banning orders to stop them turning up in Germany - he admitted Serbian officials hadn't been quite as accommodating.

He said: "It's not as good, like the cooperation with England - but it's OK."

While Both raised slight concerns over controversial England anthem Ten German Bombers, he said: "We will approach all the English supporters with an open mind.

"I expect all my colleagues to treat them fairly and proportionately, and we only will intervene in the event of any criminal or public safety incident.

"The chanting of Ten German Bombers is not criminal. It’s not forbidden in Germany... It's a stupid song.

"The English national coach said about that and he's absolutely right. It’s ridiculous. It's a stupid song, but it's not forbidden."

And Wilhelm Wessels, the Euro 2024 project manager at the City of Gelsenkirchen said: "All of the city's law enforcement partners, such as the fire brigade, the police and the municipal public order service, as well as the entire Euro staff on the grounds, are familiar with the PANAMA rules and can react accordingly.

"It was important to us to establish an awareness concept during the Euro in order to make the experience and attendance of our Euro 2024 events even safer."

Gareth Southgate's men will be looking to put their pre-tournament woes behind them on Sunday as England take the field for the first time in Germany against a tough Serbian side at 8pm UK time.

An England team - though bruised by some defensive absences - will doubtless be on the hunt for an elusive European Championship title in what could be Southgate's last competition coaching his country.