The British government has removed Spain from its "air bridge" list of countries, reintroducing a mandatory two week quarantine.
Anyone arriving in the UK from Spain must now self-isolate for 14 days or face a £1,000 fine.
This has thrown summer holiday plans into chaos, as Brits currently in Spain are now facing a two week quarantine they had not planned or prepared for.
The FCO has also changed its advice for Spain, and now advises Brits against all but essential travel to the mainland.
The Canary and Balearic Islands are, however, still considered safe by the Foreign Office.
This means Brits can still go on holiday to the Spanish islands - as long as they're prepared to quarantine when they get back.
Here are the rules explained:
What are the rules for mainland Spain?
The FCO currently advises against all but essential travel to mainland Spain, meaning you should not go there for a holiday.
Your insurance will not be valid, meaning you will not be covered in the event of an accident or emergency - even if it has nothing to do with coronavirus.
From Sunday 26 July, anyone arriving into the UK from Spain will have to self-isolate for 14 days. They will only be allowed to leave the house for medical assistance, to attend court, or to go to a funeral.
They can leave the house to buy food - but only if there is no other way they can get supplies.
What are the rules for the Canary Islands and Balearic Islands?
The same quarantine rules apply to travellers coming into the UK from the Spanish islands - including Gran Canaria, Ibiza, Lanzarote and more.
Anyone who has been on holiday at these destinations will have to self-isolate for 14 days when they get back.
However, the FCO does not currently advise against travel to either the Canary Islands or Balearic Islands.
This means you can still go on holiday to these destinations - as long as you're prepared to quarantine when you get back.
If you cannot commit to 14 days self-isolation (if you have work commitments, for example), then you must not go on holiday.
Do I have to quarantine when I arrive in Spain?
The Spanish government does not currently require tourists to quarantine when they arrive - but this could change at very short notice.
There are currently temperature checks at the airport, and visual assessments made by staff.
Can I get a refund if I no longer wish to travel?
While the FCO now considers travel to mainland Spain dangerous, many airlines are proceeding with flights as normal.
Some are offering customers the option to rebook their flight without paying a change fee, but you may not be entitled to a refund.
You should check with your airline to find out your options.
