The Heathrow Express, Britain’s most expensive train link, gets more complicated to use from 20 May – with some passengers facing higher fares.

The standard £22 fare for the 15-mile, 15-minute journey between the airport and London Paddington remains the same. But the times for the peak £25 fare are shifting for morning travellers. Instead of 7-10am, the higher price applies 6.30am-9.30am, penalising passengers travelling early; conversely those using the service after 9.30am will save.

The train operator says: “We are making changes to some of our terms and conditions to bring us in line with other national rail services.”

The evening peak remains the same at 4-7pm. Booking three months ahead for travel at weekend, fares are available for £5.50. Under-16s travel free on the Heathrow Express.

Travellers using the link will find an extra hurdle in the shape of ticket barriers at the airport stations. At present all ticket checks are carried out on board.

But from 20 May the slower Heathrow Connect service – also departing from Paddington, but calling at intermediate stations – is replaced trains run by Transport for London (TFL). As part of this change, gates that accept Oyster and contactless cards are being installed.

Terminal 4, which has not had regular direct trains from London since Terminal 5 opened a decade ago, will once again be connected to Paddington. Trains via the central area will run every half hour. Although the journey time will increase from 27 to 35 minutes, there will no longer be the requirement to change trains.

The one way fare for the journey from Paddington to Terminal 4 falls by more than half from £22 to £10.30.

Passengers between Heathrow’s central area, serving Terminals 2 and 3, and Terminals 4 and 5, will continue to be able to travel free.