British tourists to Spain could face airport queues of five hours or more after a no-deal Brexit, according to analysis by Which?, and the consumer group suggests travellers should take food, water and even nappies to survive prolonged delays.

Alicante airport, which serves Benidorm and other Costa Blanca resorts, is likely to be the worst-affected airport, and Which? said visitors to Tenerife, Lanzarote and Málaga were also facing “life in the slow lane”.

It calculated that if airports spent only 90 seconds making extra checks on each UK passport, it would take a single passport lane in an EU airport five hours longer to process a Ryanair flight with 189 UK passengers on board.

Alicante is likely to be worst hit because 43% of its arrivals are from the UK. Even in February, the airport processes as many as 10 planes from the UK in a single hour. In total, 2.9 million British passport holders go through the airport each year.

Portugal plans special UK lanes at Faro airport in the Algarve and Funchal, the capital of Madeira, to provide fast-track access for British passport holders, irrespective of a Brexit deal or no deal, but Spain has yet to formally reveal its position.

Rory Boland, the travel editor of Which?, said: “Airports can be chaotic at the best of times but if additional checks at passport control 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 Which? analysis of queues and processing time was based on data from the European Tourism Association (ETOA).

The official UK government advice in the event of no deal is that British tourists will have no right to use the separate lanes for EU, EEA and Swiss nationals, may be asked to show a return or onward ticket and may face checks to ensure they have sufficient funds for the duration of their visit.

Aena, Spain’s biggest airport operator, said it did not envisage chaos at airports this summer because too much was at stake. It said: “Aena does not consider that the most pessimistic scenario will occur. We believe that once the starting uncertainty is overcome, United Kingdom traffic can continue being strong in both the middle and the long term.”