A man suspected of selling fake coronavirus test certificates was arrested at Luton airport, police said.
Several countries served by the airport require international arrivals to provide proof of a recent negative coronavirus test, including Italy, Bulgaria and Romania.
The suspect, in his 30s, was arrested at 8pm on Wednesday on suspicion of fraud by false representation, Bedfordshire Police said.
He was released under investigation.
Detective Sergeant Tom Hamm of Bedfordshire Police said: "If you are travelling abroad to a country that requires proof you are fit to fly, you can only obtain this from an approved test provider.
"Unfortunately, fraudsters have seen the ongoing pandemic as an opportunity to prey on people, and if you are approached by someone offering to sell certificates who is not an authorised provider, please report it immediately."
Luton airport operations director Neil Thompson said: "We work closely with Bedfordshire Police to ensure we keep our staff and passengers safe at all times.
"Everyone working at the airport is trained in general security awareness and along with other measures in place, anyone attempting to commit crime at LLA (London Luton Airport) has a very strong chance of detection.
"We will always take a zero tolerance approach to such behaviour and will support police in any action they take."
Anyone with information about the incident is asked to report it via Bedfordshire Police's online reporting system quoting reference 319 of January 20, or contacting Crimestoppers anonymously on 0800 555 111.