The Balearic and Canary Islands have been added to the list of areas where all non-essential travel should be avoided, the Government has said.
The move comes after Downing Street warned "no travel is risk-free" after a coronavirus quarantine requirement for people arriving in the UK from Spain was reintroduced.
The Foreign and Commonwealth Office (FCO) updated its travel advice for visits to Spain, saying: "The FCO advise against all non-essential travel to Spain, including the Balearic and Canary Islands, based on the current assessment of Covid-19 risks in the country."
An FCO 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."
The announcement came after the Prime Minister's official spokesman said decisions on border measures and travel advice "can be changed rapidly if necessary to help stop the spread of the disease".
He went on: "Unfortunately no travel is risk-free during this pandemic and disruption is possible and so anyone travelling abroad should be aware that our travel advice and exemption list is under constant review as we monitor the international situation."
The decision comes after the Spanish government said it was in talks with the UK about excluding the Balearic and Canary Islands from its quarantine measures.
But Health Minister Lord Bethell said: "Within individual countries there is no way for us to control intra-country transport, it is therefore very difficult and challenging to have a regional exemption list, and that is why we've not been able to give exemptions to the Balearics."
The announcement happened amid fears more European holidays could be thrown into disarray this summer with reports of potential new coronavirus lockdowns in France and Germany.
The change in the UK's quarantine policy on Spain over the weekend is being met with frustration from holidaymakers and travel firms.
Transport Secretary Grant Shapps is coming home early from a trip to Spain after the quarantine decision.
Mr Shapps told The Sun: "I think it's right to get back to work in the UK as soon as possible to help handle the situation.
"The sooner I get back from Spain myself, the sooner I can get through quarantine.
"So, I'm leaving my family to travel back to the UK on Wednesday."
Cabinet Office Minister Michael Gove, who said he may have to cancel his planned trip to Ibiza, described it as a "very serious situation".
Downing Street added that holidaymakers who miss out on work because of the quarantine period may be eligible for Universal Credit or employment support allowance but not statutory sick pay.
Andrew Flintham, managing director of TUI UK and Ireland, called for a "more nuanced policy" to include rules based on regions as well as countries.
Tui has suspended all holidays to mainland Spain up to and including August 9.