Holidaymakers heading to Greek islands face disruption after an Athens minister warned that some were "one step" away from tougher Covid restrictions.
Nikos Hardalias, the Greek deputy civil protection minister, said Mykonos and Ios were on the brink of fresh curbs due to a surge in infections. Case rates have soared among people aged 20 to 30.
Mr Hardalias warned that the situation on the islands of Zakynthos, Tinos, Lefkada, Santorini, Paros and Rhodes was also worrying.
Curbs including a curfew and a music ban were imposed on Mykonos two weeks ago following a 248 per cent rise in confirmed cases. The measures were lifted on Monday following negative publicity and a wave of cancelled bookings, but could be reimposed.
Mr Hardalias's comments dovetailed with the arrival of 185 police officers on Mykonos on Thursday to step up checks at nightspots – up from the 56 stationed there last summer. An additional 30 were sent to Ios, along with security officials and undercover agents.
It came after the European Centre for Disease Prevention and Control marked Greece's south Aegean islands dark red in the wake of a spike in virus infections, meaning EU citizens are advised against non-essential travel to the area.
Meanwhile, British families hoping to visit Italy in the coming weeks will still be forced to isolate for five days on arrival, even if fully vaccinated, after Rome confirmed it would not reciprocate the UK's move this week to allow EU visitors to skip quarantine. The measures in Italy will stay in place until at least August 30.
Paul Charles, of travel consultancy The PC Agency, said it was "highly embarrassing" that the Government had "not been able to bring countries with them and therefore help British consumers".
His intervention came as Grant Shapps, the Transport Secretary, appeared to slap down Dominic Raab, the Foreign Secretary, over the latter's suggestion earlier this week that France had been put on the UK's "amber plus" list due to Covid variants identified in Reunion, an island 6,000 miles from Paris.
Mr Shapps told Sky News the move had been made due to "overall concern" about the beta variant in France, including "an issue in particular in northern France" rather than Reunion.
Huw Merriman, the Tory chairman of the Commons transport select committee, told The Telegraph: "We need to see the evidence base for these decisions. A lot of it doesn't stack up when you deconstruct it. There doesn't seem to be any sort of logical pattern. These decisions seem haphazard, and don't inspire me with great confidence."
The next review of the Government's traffic light travel list is due to take place next week, when France could move off the "amber plus" list which means fully vaccinated Britons must isolate at home for 10 days upon return.
On Friday, an analyst warned that ministers may add Spain to the "amber plus" list. Data expert Tim White said his analysis was "bleak", highlighting that NHS Test and Trace figures showed 2.9 per cent of people arriving in England from Spain in the first three weeks of July tested positive for Covid.
Mr White said: "More worryingly for Spain is that three per cent of the samples had a variant not widespread in the UK."
It is also possible that ministers could move nations on to an "amber watchlist", designed to signal to holidaymakers that each country could switch imminently to the red list.
Scientists advising the Government have warned that any increase in foreign travel this summer is worrying, while the autumn could prove a "particularly risky point" for the nation.
Advice given to ministers earlier this month by the SPI-M sub-group said: "Any increase in foreign travel over the summer and the return of international students to universities in the autumn is of particular concern."