Spain has been removed from the government's travel corridors exemption list.
This means if you arrive in England, Wales, Scotland or Northern Ireland from Spain on or after July 26 2020, you will need to self-isolate.
Brits currently holidaying in Spain will have to quarantine for 14 days upon their return – unless they're back by midnight tonight.
The so-called "travel corridor" with Spain has been shut down after the country reported more than 900 new daily infections over the past two days.
Tourists who are already in Spain can stay there for the remainder of their holiday but will now have to self-isolate upon their return.
They are encouraged to follow the local rules, return home as normal and check the Foreign and Commonwealth Office's travel advice pages on the government's website for further information.
The FCO is now advising against all but essential travel to mainland Spain.
Why has Spain been removed from the exemption list?
An escalation in coronavirus cases has prompted the decision to remove Spain from the government's safe country list.
The updated advice is based on evidence of increases in cases of the deadly virus in several regions, but specifically in Aragon, Navarra and Catalonia, which includes the cities of Zaragoza, Pamplona and Barcelona.
Spain has warned a second wave of coronavirus could be on the horizon, with cities including Madrid and Barcelona reporting a rise in cases.
What if I have a holiday booked?
The FCO is not advising those already travelling in Spain to leave at this time.
Travellers should follow the advice of the local authorities on how best to protect themselves and others, including any measures they may introduce in a bid to control the virus.
If you are returning from Spain on or after July 26, you will need to quarantine on your return to the UK but the FCO is not advising you to cut your trip short.
The government advises that you should contact your tour operator or airline if you have any questions about your return journey.
Airlines UK, the industry association representing UK-registered carriers, said in a statement: "The advice is clear that people already in Spain should return home as per normal and check the FCO travel pages.
"Public health must be the priority but this shows why regional travel corridors need to be considered, so that travel to safe parts of a red country can continue.
"We also need to see the introduction of testing at UK airports so that those who are Covid negative can continue to travel without the need to self-isolate upon arrival.
"We will continue to work closely with Government to protect public health whilst keeping air travel and the wider economy open."
What if I'm planning a holiday?
The Foreign and Commonwealth Office now advises against all non-essential travel to mainland Spain based on the current assessment of coronavirus risks.
This doesn't mean it's illegal to go there, but it's a warning that you could be at higher risk of catching the potentially deadly virus.
Sometimes it is harder to get travel insurance if you're going to a country against official advice, and there may be other knock-on effects.