Travellers buying their foreign currencies at UK airports are being offered as little as 86 euro cents to the pound.
Foreign exchange broker FairFx, which carried out a survey for the BBC, said this rate, from Moneycorp at Southampton airport, was the worst at any airport bureau de change.
The average euro rate across 16 big UK airports was higher, at 95 euro cents to the pound.
Ten months ago the average at these outlets stood at 99 euro cents.
The best euro rate for tourists detected in the airport survey was €1.05 from Travelex at Newcastle airport.
FairFX chief commercial officer James Hickman said the fact that airport rates are so low – much worse even than at high street banks – shows that the bureaux de change firms are taking advantage.
“In reality they are ripping off the customer, who is effectively captive as they have nowhere else to buy their money at an airport,” he said.
“At most airports and terminals individual companies have a monopoly.
“They should be regulated as there is simply no justification for charging someone 14% [the average margin between the tourist and money market rates] to change their pounds to euros,” he added.
That margin is as high as 26% at Moneycorp’s Southampton airport outlet.
Pauline Maguire, Moneycorp’s retail director, said: “The reason for our higher airport rates is the significant cost associated with operating there – from ground rent and additional security, to the cost of staffing the bureaux for customers on early and late flights.
“An easy and more cost-effective way for customers to buy travel money is to pre-order online and collect at the airport.”
The average tourist rate for the pound against the US dollar is also very low.
Currently the average is $1.12 to the pound at UK airports, ranging from $1.05 at ICE at Norwich airport to $1.15 from Travelex at Heathrow Terminal 3.
Koko Sarkari, chief executive of ICE, which runs bureaux de change at Belfast, Birmingham, Heathrow and Luton airports, denied that his firm was exploiting a captive market.
“We work hard to keep our prices fair and competitive around the world,” he said.
“However, due to differences in distribution, costs of operation, regional competition and other factors such as ongoing volatility in the market, as we are experiencing now, online prices may not be the same as our ICE branch prices and prices may also vary between branches because of these factors.”