The Foreign and Commonwealth Office and the Treasury are putting measures in place to help evacuate thousands of expatriates living in Spain and Portugal in case they are stranded no access to their savings.
The two countries, which both have sizeable British populations, were among those made vulnerable by the "sustained deterioration" in funding.
Spain was warned by credit rating agency Fitch that it was facing a debt downgrade along with Italy, while Ireland, Belgium, Slovenia and Cyprus were also given the warning.
Meanwhile, around one million Britons live in Spain with around 50,000 in Portugal.
The Foreign Office said it was concerned they could be cut off from their accounts if the countries' banks called in loans.
A source told the Sunday Times the Government was considering chartering planes, ships and coaches to bring expats back to the UK.
“The nuclear scenario would be having thousands of Brits stranded at the airports in Spain and Portugal with no way to get money from the cash dispenser and no way to get home. Who would be blamed for this? The Foreign Office," an official said.
“We are looking at how we can help evacuate them if the banks in Spain and Portugal collapse, getting people cash, things like that, sending planes. We did similar things in Lebanon in 2006. We are coordinating with the Treasury.”
Financial aid could also be sent to expats, many of whom are retired and living on small incomes.
A Treasury spokesman said: "Of course we plan for a range of contingencies. We are not going into the specifics of what we are planning for."
Last month, it was reported that the Foreign Office had asked embassies and consulates for contingency plans for rioting and social unrest in countries most affected by the eurozone crisis.
Diplomats were told to prepare for an evacuation of tens for/of thousands of British citizens as a banking collapse could mean they would be unable to withdraw cash.
An FCO spokesperson said: "Officials continue to contingency plan for a range of possible scenarios"
Let us just hope that it doesn’t come to this.