Online train ticket retailers are using so-called drip pricing with booking fees of up to £6.45 per transaction, a regulator has found.

The Office of Rail and Road (ORR) said the companies must ensure their booking or finder’s fees are included in upfront prices.

Drip pricing involves fees being added to advertised low prices.

The ORR reviewed the websites and apps of 19 third-party train ticket retailers.

Twelve were found to charge booking fees, and seven of these did not include this amount in the upfront price.

The ORR’s review found booking fees ranged from 45p per ticket to £6.45 per transaction.

Finder’s fees were 10 to 15 percent of the savings made on split tickets, which involve purchasing multiple tickets for single journeys to cut the overall price.

ORR director of strategy, policy and reform Stephanie Tobyn said: “Consumers can now purchase rail tickets from a wide variety of websites and apps.

“This report highlights that some online retailers are not as transparent as they need to be when it comes to how they display or provide information on additional fees.

“We want to ensure consumers are provided with timely and relevant information when making purchase decisions and that drip pricing does not undermine consumer confidence when purchasing rail tickets online.”

The 12 retailers found to charge booking and/or finder’s fees were MyTrainTicket, Omio, Rail Europe, Railboard, Raileasy, Sojo, Split my fare, Train Hugger, Trainline, Trainpal, Trainsplit and TrainTickets.com.

A Department for Business and Trade consultation into price transparency, including drip pricing, closed in October.

It comes after Express.co.uk reported that passengers stuck for more than three hours on dark, cold trains while receiving no information may be liable to pay up to £26 for the experience.

Passengers who were trapped on London’s Elizabeth Line trains for up to three hours or more may be fined up to £26 for exceeding maximum journey times.

Thousands of people were stranded on services for hours after damage to overhead electric cables in west London on Thursday (December 7). About seven trains were affected, operated by the Elizabeth line, Heathrow Express and Great Western Railway (GWR).

Images and footage shared on social media on Thursday night showed commuters sitting in dimly lit carriages suffering from power outages, before they were eventually evacuated. There are reports some broke their way out of carriages and walked down the tracks in the dark.