Following the downgrading of Belgium’s credit rating, the Foreign Office is advising its embassies to prepare contingency plans for the possibility of the collapse of the euro.

You would expect the Foreign Office mandarins to be prepared for every eventuality – but here’s a doomsday scenario which might just happen.

British embassies are now taking active steps to prepare for the possibility of the euro collapsing – something that’s no longer as inconceivable as it once was.

The Foreign Office is preparing contingency plans to help expats from the Costa del Sol and the Algarve who could be stranded without cash – or caught up in riots and civil unrest.

In the historic town of Bruge, they are preparing for the annual ice festival. But it is a chill of a different kind that is preoccupying the leaders of Belgium.

The country’s credit rating has been downgraded and that is causing shockwaves throughout the eurozone.

Belgium is no fragile Mediterranean economy. It’s one of the founding members of the European community and to some economists its downgrade makes the collapse of the euro much more likely – and Britain can’t escape the consequences.

“I think we would be talking about defaulting and mass bank runs on a scale unparalleled in human history,” said Dr Andrew Lillico of the Europe Economics. “We’ve never had events of this sort in the period where we have banks of this sort that we have now.”

It’s been known for some time that the Treasury officials have been planning for the possible break up of the euro but it now looks as if other Whitehall departments are doing the same. At the Foreign Office they’ve been reminding embassies that they could have British citizens without access to their bank accounts or in danger of getting involved in civil disturbances.

The crisis has already given a foretaste of what could be ahead with violent protests against Greek austerity measures and similar scenes of the streets of Italy.

The Foreign Office tonight declined to discuss any instructions given to embassy staff, referring inquiries to the Treasury.

A spokesman there said “You would expect every good government to have contingency plans in place to cover a range of eventualities and risks, and this government is well prepared for any eventuality.”