London's transport watchdog repeated its warning to passengers on 8 May not to get caught out by 'device clash' or else risk being overcharged for their travel.

The latest call by London TravelWatch comes after a Freedom of Information Act (FOI) request made by a member of the public to Transport for London (TfL) revealed that TfL is refunding the equivalent of over £200,000 a year to passengers who have fallen foul of the problem.

Device clash happens when a person at the start of their journey uses one payment device (such as a digital wallet on their mobile phone) linked to their bank account and then uses another linked device (such as a smartwatch or contactless bankcard) at the end of their trip. 

Although both devices are linked to the same bank account, for security reasons each one has a separate identity number. 

TfL's systems are unable to recognise that the transactions belong to the same user, treating them instead as two separate, incomplete trips, each charged at the maximum fare.

Mr Paul Harper, who discovered the extent of the issue through his FOI request, said: "I was stunned by how much was taken out of my bank in such a short space of time. One journey from Watford to London and back cost £42 which is ridiculous.

"In fairness, TfL refunded me very quickly within a week. But it did make me wonder how many other passengers are being overcharged without knowing, particularly people visiting the city for a day or weekend who probably pass it off as expensive travel."

Michael Roberts, CEO of London TravelWatch, said: 'The level of TfL refunds is startling, but could be the tip of the iceberg as it doesn't reflect the impact of device clash on passengers who just don't realise that they have paid over the odds.

"We need TfL, banks and tech companies to re-double their efforts to find a permanent fix to this problem and to do more in the meantime to advise people to use just one device. 

"Until then, we urge people who pay for travel using smart devices to check your bank statements regularly so as not to lose out."