Ryanair last week told passengers that online check-in was only available between seven days and two hours before departure for those not taking its regular or premium seat reservation option, costing €5 or €10. Those opting to pay extra can check in from 30 days before.

Previously, Ryanair allowed non-reserved seat boarding passes to be printed 15 days before departure, which catches a normal fortnight family holiday.

However, the change means agents packaging a week’s holiday with Ryanair flights cannot now issue the return boarding card before clients leave the UK.

One agency, Thorne Travel, which is close to Prestwick airport, has told clients: “To ensure you get the best customer service for all flights booked with a six day or longer duration, we will require you to pre-book your seats.”

Agency owner Shona Thorne said hotels had been happy to print boarding cards for existing bookings, but that this would create problems in the future.

“Hotels are not going to be happy,” she said. “We’ve done this before for customers going for three weeks and most hotels have been quite comfortable doing that, but we have a group of 30 going soon - do they want to do that? No.”

Thorne said the agency would be greatly affected, being 10 minutes from Prestwick. “To change the rules on existing bookings is wrong,” she said.

Ryanair charges £40 to print boarding cards at the airport, meaning a family of four caught unawares faces a £160 bill at the end of their holiday.

The airline’s changes come only weeks after it launched a charm offensive, promising to be less obstructive. A Ryanair spokeswoman said check-in times had been extended for those who purchased allocated seats.

“Customers who don’t wish to pay for a premium or regular allocated seat can check-in online between seven days to two hours prior to each flight, and will be allocated a seat free of charge,” she added.

Helder Lemos, who runs Gallivant Travel Agency near Stansted, said Ryanair had “reverted back to type”, adding: “What comes to mind immediately is the saying ‘the leopard never changes its spots’.

It found a subterfuge to force ancillary revenues and annoy the customers.”