A no-deal Brexit could see UK travellers to top European holiday destinations face hours of delays because of additional entry checks at EU airports.

The warning comes as part of an investigation by consumer group Which? Travel identifying EU airports where UK passport holders could face disruption.

Alicante in Spain faces being worst affected as almost half (43%) of all passengers entering the airport arrive from the UK.

It would need staff and resources to deal with an additional 201 hours of immigration checks, on average, every single day in a no-deal Brexit.

Six of the top ten busiest airports for UK arrivals are in Spain. Tenerife South, Lanzarote, Malaga, Ibiza and Palma airports all potentially face severe difficulties if a contingency plan is not put in place to manage the new requirements, according to the consumer watchdog.

The Spanish government has yet to announce how it will tackle additional immigration checks.

This means that immigration officials will be obliged to check UK visitors’ passport validity, passport expiry date, purpose and length of stay, and whether visitors can support themselves financially.

The European Tourism Association has estimated that additional checks required in a no-deal Brexit could add an extra 90 seconds for each UK passport holder.

It would take a single passport lane in an EU airport an extra 17,010 seconds, or nearly five hours, to process 189 passengers on a single Ryanair flight, if all arrivals had UK passports.

The additional processing time will lead to further delays with each new flight arriving.

When Alicante airport’s arrivals were checked by Which? last Friday, as many as ten aircraft arrived from the UK in a single hour.

Although Faro airport in Portugal has the biggest proportion of UK arrivals overall, the Portuguese prime minister has already announced plans to ease congestion by opening special fast-track lanes at both Faro and Funchal airports.

A European Commission spokesperson confirmed to Which? that “as of the withdrawal date, UK nationals will not be entitled to use the separate lanes provided for EU/EEA/CH citizens”.

It also stated that British holidaymakers “will be subject to thorough checks of all entry conditions for third country nationals upon entry”.

Spain’s national border agency, the Guardia Civil, did not respond when asked whether it plans to add extra facilities or employ more staff.

Which? Travel editor Rory Boland said: “Airports can be chaotic at the best of times, but if additional checks at passport control in Spain, Italy and other popular EU destinations are implemented in the event of a no-deal, it seems that very long queues are going to be an unwanted side effect.

“Until there is a deal or these airports announce simpler arrangements, you should consider what you may need if you have to fly to them – as it is very likely that you’ll be in a queue for several hours. Make sure you have food, water and essentials for kids like nappies to hand.”

The additional hours of customs checks is based on carrying out 90 seconds of additional checks on 2.9 million passengers, and 8,000 average passengers each day.

Some of the UK arrivals will not be British. They may be EU nationals returning home, for example, and they therefore won’t be subject to additional checks. However, given the airports at the top of the list are the most popular UK holiday destinations, it is likely to the vast majority of passengers will be UK passport holders.