Currency collapses will mean a catastrophic cut in spending money for families heading abroad for the Easter holidays.
With Easter only days away, Britons are getting far fewer euros and dollars to the pound than even a few weeks ago.
The pound has fallen against most other European currencies as well, according to latest figures from Post Office Travel Money.
British travellers might have to go far afield to find favourable exchange rates, with the best bets being South Africa, Argentina and Japan.
Comparing mid-March this year with mid-March 2012, the pound has lost 5.4% against the euro and 5.5% against the US dollar.
Among countries where the pound has also fallen against the local currency are Sweden, Norway, Turkey, Bulgaria and Poland.
In contrast, Britons visiting South Africa now will get more than 17% more rand for their money than a year ago while the pound has strengthened 11.7% against the Argentinian peso and 11.6% against the Japanese yen.
Egypt, Jamaica, Sri Lanka and the Czech Republic are also places where travelling Britons will find favourable rates.
Post Office Travel Money's Andrew Brown said: "The sterling fall in recent weeks makes it doubly important for UK holidaymakers to choose destinations where resort prices are low."
He picked out Spanish resorts as a good example of this, as well as Budapest in Hungary.
Mr Brown went on: "With the falling value of sterling, we advise holidaymakers to budget carefully and to take enough spending money to cover all costs.
"The one positive of a weaker pound is that anyone who is hoarding leftover foreign currency could find they will get more pounds in their pocket if they exchange it back into sterling now."
Sean Dowd, commercial manager of holiday company Hayes & Jarvis, said: "Although sterling is volatile and holidaymakers may not be getting as much foreign currency for their pounds, the good news is that there are still a number of destinations where sterling is stronger than it was a year ago - notably in Africa and Latin America, where we have seen sales soar in recent months."
He said demand for Brazilian holidays was likely to be strong this year, particularly as prices could rise next year when the South American country hosts football's World Cup.
Mr Dowd went on: "We have also seen a 71% growth in summer bookings for South Africa, as well as an increase for Tanzania and Kenya, where sales are soaring on the back of the screening of BBC1's Africa series."