Brits have been given a fresh warning to make sure they have their passports on them at all times when travelling to Spain.
The Foreign Office has urged tourists to remember that Spanish police have the legal right to demand to see ID.
Anyone who fails to do this can be detained.
Thousands of football fans set to converge on capital Madrid for Liverpool's clash with Atletico later this month.
Most visits are trouble-free, but Britons are now legally required to present their ID if requested by a police officer.
A driver's licence is not suitable – only the original passport or a clear photocopy will suffice.
However, police have the right to accompany foreigners back to their accommodation and request to see the original document.
Spanish police routinely conduct passport sweeps of public events to locate criminals or people in the country illegally. If an unruly Brit refuses to co-operate, they could find themselves in a holding cell.
"The police have the right to hold you at a police station until your identity is confirmed," the Foreign Office warns on its website.
"Always take care of your passport, as obtaining a replacement is costly and time-consuming.
"Remember to keep a photocopy or scanned copy of your passport somewhere safe."
Visitors have also been reminded to keep an extra watchful eye on their possessions at airports, train stations and on public transport to avoid their bags being snatched by pickpockets.
It is also vital to keep a copy of your passport somewhere safe and never hand over a wallet if requested by someone claiming to be an officer.
Police officers have the right to stop people from taking photos or filming if they consider that their personal security or that of a police operation or secured area could be compromised as a result. Doing so can be met with severe penalties.
