The EU has boosted hope for summer holidays with plans to allow tourists back soon.
And those with just one jab may be able to travel if they are from areas with low Covid rates.
Commission President Ursula von der Leyen said: “Time to revive EU tourism industry.”
Boris Johnson urged “caution” to avoid an influx of variants.
Ursula von der Leyen’s bid to open up Europe to tourists this summer will be welcome news for Brits starved of sunshine holidays and worn down by a year of lockdowns.
The EU Commission president unveiled plans to welcome back people from countries outside the bloc with low Covid case rates, even if the have not had both doses of the vaccine.
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But Boris Johnson warned Britain would be “cautious” to avoid a glut of cases from abroad. EU member states are due to start discussing the proposals on Tuesday. Sources have suggested travel could open up in June.
Ms von der Leyen tweeted: “Time to revive EU tourism industry and for cross-border friendships to rekindle…safely.”
Mr Johnson said: “We do want to do some opening up on May 17 but I don’t think the people of this country want to see an influx of disease from anywhere else. I certainly don’t.
“And we have got to be very, very tough, and we have got to be as cautious as we can, whilst we continue to open up.”
Keir Starmer also urged caution approach as he warned against a repeat of last summer’s holiday chaos, when the things were “chopping and changing on a daily or even weekly basis”.
The Labour leader said: “We need to be very careful. It’s clear that the virus is increasing in some countries.”
Under the EU’s plans, tourists who have had both jabs for at least 14 days would be allowed in for holidays – no matter where they come from.
Those who are not fully vaccinated will be allowed in if their country has a “good situation” with Covid cases.
This could mean Brits under 40, who will have to wait most of the summer to get their second dose, could be granted entry.
Children should be able to travel with their vaccinated parents if they have a negative PCR test taken 72 hours before arrival.
But families will still have to quarantine when they get back unless their destination is on the UK’s green list of countries, to be unveiled this week.
The EU’s list of safe countries currently only has seven members and does not yet include the UK.
But officials are recommending those with a 14-day case rate below 100, rather than 25, be allowed on the list. EU figures suggest the UK’s 14-day case rate is around 46 per 100,000 people
But Brussels also warned it could impose a sudden temporary “emergency brake” to stop arrivals from areas with new waves of the disease.
Thomas Cook chief executive Alan French said he expected most popular holiday destinations in Europe to open.
He added: “When we look at what is going on in those countries, both in terms of infection rates and how they are preparing for holidaymakers, I think there is great progress being made.”
A cross-party group of MPs has warned restrictions on foreign holidays should stay in place to protect the UK from new variants.
It comes as the number of jabs given out in the UK passed the 50 million milestone - while a quarter of the adult population have had both doses.
Health Secretary Matt Hancock said: “This is so important of course because it is a life-saving vaccine that is our route out of this pandemic.”
Just one Covid death was recorded on Monday as infection levels continued to fall.
