The UK has updated its advice against all non-essential travel to Spain to include the Balearic and Canary Islands following a rise in coronavirus cases.
Foreign Office guidance was changed on Monday to include both mainland Spain and islands such as Ibiza and Tenerife.
Holiday firm Jet2 has told passengers not to go to the airport after cancelling flights to all Spanish destinations on Tuesday.
The change is in addition to the self-isolation policy that began on Sunday.
The amended advice came after calls for clarity from travel companies and as airlines announced sweeping flight cancellations.
Jet2 said it will not be operating flights to Tenerife, Fuerteventura, Gran Canaria, Lanzarote, Majorca, Menorca and Ibiza, or to mainland Spain, but will be running a schedule of flights back from those destinations on Tuesday.
Holiday operator Tui, meanwhile, said it would cancel all its packages to the Balearic and Canary Islands until 31 July and to mainland Spain until 9 August.
Travellers returning to the UK from anywhere in Spain must now self-isolate for 14 days at a registered address.
A Foreign Office spokesman said: "We have considered the overall situation for British nationals travelling to and from the Balearic and Canary Islands, including the impact of the requirement to self-isolate on return to the UK, and concluded that we should advise British nationals against all non-essential travel to the whole of Spain."
Speaking earlier, Boris Johnson's official spokesman warned "no travel is risk-free during this pandemic".
The rate of infection in Spain is 35.1 cases per 100,000 people, while the UK is at 14.7, according to the latest figures from the European Centre for Disease Prevention and Control.
Data up to 19 July suggested there were lower rates of infection in the Balearic and Canary Islands than in mainland Spain.
Meanwhile, a government source told the BBC that the Spanish government was lobbying for the Balearic and Canary Islands to be exempt from the quarantine policy, and that discussions on the matter had taken place.
Spanish Prime Minister Pedro Sanchez described the decision to impose a 14-day quarantine as an "error" as it applied to the whole of Spain, rather than affected regions, the Reuters news agency reported.
Among the thousands affected by the change in travel advice was Tom Clasby, who had checked into an airport hotel near Stansted with his fiancé, their two daughters, and other family members, ahead of a holiday to Majorca.
Mr Clasby, 26, was due to depart at 06:55 BST on Tuesday but now faces having to return home to Bury St Edmunds.
"We're in a situation where we can't do anything yet and I don't actually know what to do. The poor little girls have been so excited for this holiday - it's the second holiday this year we've had cancelled," he told the BBC.
"We are just very disappointed, the girls will be so upset in the morning."
Another would-be traveller, Rachel Warren, 43, said her bags were half packed for a planned trip to Tenerife on 31 July when she received a text message saying her trip was cancelled.
It's the third holiday she's had called off this year.
"I was supposed to be going to Mexico, changed it to Ibiza and then amended the booking for a third time when they all got cancelled. I thought Tenerife was going to be third time lucky and now this has happened," she said.
"I can try and rebook; god knows where, or how, or when!"
Also affected was Transport Secretary Grant Shapps, who flew to Spain on Saturday despite knowing a decision on the quarantine policy was due.
Mr Shapps said in a statement he would return to the UK this week in order to complete his quarantine and would return to work as soon as possible.
And Cabinet Office Minister Michael Gove said he cancelled a holiday to the Balearics after the change to quarantine rules was announced on Saturday.
EasyJet, British Airways, and Ryanair said they would continue to operate full schedules of flights to Spain, though EasyJet said its holidays would be cancelled for the next few weeks.
The UK imposed the restriction over the weekend after a spike in infections in some Spanish regions, including Catalonia, where Barcelona is located, and Aragon.
The French government has told its nationals to stay away from Catalonia, while Norway has imposed a new 10-day quarantine on all travellers arriving from Spain.
It comes as a further seven people with coronavirus were reported to have died across all settings in the UK, according to latest government figures - bringing the UK's death toll to 45,759.
The government also said in the 24-hour period up to 09:00 BST on Monday, there had been a further 685 lab-confirmed cases. The UK's total is 300,111.