Holidays can cost 50% more if you book on a computer, not a smartphone app

And one London hotel even charged £200 extra per night, a Mail on Sunday investigation has found.

Prices of rooms for a family of four in the UK and Europe during half-term were an average of 16 per cent more per night – nearly £50 – if the booking was made on a ­laptop or desktop computer.

In the worst example, The ­Cumberland hotel in London charged a family of four £388 for booking two rooms via the Booking.com smartphone app, but £588 on its website – a 52 per cent hike.

Experts said the pricing system meant families were 'unwittingly and unfairly' paying over the odds.

We compared 35 hotels listed on Booking.com in popular half-term destinations in the UK and abroad, including Tenerife and Majorca. We looked at the rates for a family of three booking one room, and a family of four booking two, for the night of October 31.

In total, 30 out of the 35 increased prices between 4 and 52 per cent, with a family of four booking two rooms forking out an average of £49 more per night through the website, while a family of three booking one room paid an average of £36 more.

We found a family of four was being charged £108 more – £538 – on the website for two rooms at the Sheraton Grand Hotel in Edinburgh. The price of an apartment at the Royal Tenerife Country Club was 30 per cent higher – £237 – compared with £182 on the app. And it was 25 per cent more at Melia Palma Marina, Majorca – £257 instead of £206 – for a family of four booking two rooms.

For two adults with no children, just six hotels charged an average of 10 per cent more on the website.

Although some of the cheaper app prices were labelled 'mobile-only', many were not. And there was no indication to website customers that app prices could be cheaper.

Consumer expert Helen Dewdney, of The Complaining Cow website, described the practice as 'utterly bizarre'. Rory Boland, ­editor of Which? Travel, warned: 'Families are unwittingly – and unfairly – paying higher prices for their ­holiday.'

A Booking.com spokesman said hotels set their own prices, adding: 'Our accommodation partners offer mobile-only rates as a way to appeal to customers.'

By ROSIE TAYLOR