Ryanair has warned passengers booked to fly to Spain this summer that they may face extra charges.

The airline has emailed passengers due to fly from Spanish airports to warn them they face paying the cost of an increase in Spain’s airport fees, proposed in the country’s Budget.

The message says: “We may be forced to debit passengers for any government-imposed increases in airport charges prior to your travel date”.

The message cites its rule that says “if any such tax, fee or charge is introduced or increased after your reservation has been made you will be obliged to pay it (or any increase) prior to departure”.

Ryanair said Spain was proposing to double the departure tax on flights out of Madrid and Barcelona airports, and impose smaller increases elsewhere.

It is thought the increased levies could lead to passengers being charged an additional £4 to £8 each.

Ryanair said: “Any passengers who have already booked to travel later this summer will have to pay these higher fees, if the Budget is approved by the Spanish parliament.”

The no frills carrier’s chief executive Michael O’Leary said the warning arose from a draft budget presented by the Spanish government, with what he called the “ludicrous suggestion” that charges at the two main airports in Madrid and Barcelona could soar.

“It’s a bit uncertain at the moment but it looks like the Spanish government are going to double the airport fees overnight the day the budget gets passed,” he told the Independent.

“We have already taken a number of millions of bookings for passengers intending to travel to these airports this summer, and if they double the taxes we will be sending them a bill for the increased taxes or debiting their debit and credit cards”.

O’Leary said passengers who object would get a full refund: “You can of course reject that additional payment, cancel your flight and then not fly with us if you so wish.  But we’re not going to be funding the Spanish government’s taxes.”

British Airways – which flies from London to Madrid and Barcelona – said it would absorb any increase, as it did on existing bookings when Air Passenger Duty was doubled.