Britons’ summer holiday plans were given a major boost on Monday, as the EU confirmed vaccinated travellers will be able to fly to Europe from June, though it’s understood the UK could give the green light to travel to fewer than 10 countries.

The changing quarantine requirements for popular holiday destinations looks set to make 2021 the year of the last-minute booking.

The EU will reopen to holidaymakers from countries with low Covid infection rates such as the UK, and to anyone who has been fully vaccinated, by the start of June under a European Commission plan.

A traffic light system will be announced this week under which countries will be added to green, amber and red lists, with different rules regarding issues such as quarantine of returning travellers for each list.

Senior UK government sources said the number of destinations to which Brits can travel quarantine-free from 17 May could be in single figures – despite pressure from Conservative MPs for the UK to greenlight travel to the whole of Europe as vaccine rates improve. A significant number of countries on the list are unlikely to be major holiday destinations, one source warned.

One Whitehall source said changes could come quite rapidly over the summer as the list of green countries is reviewed every three weeks.

“It will be a cautious approach, but then things could start to change quickly,” the source said.

On Monday, Johnson said that he did not want to see an “influx of disease” once international travel resumes, which is why the government said it is being “as cautious as we can” with the roadmap.

“We do want to do some opening up on 17 May but I don’t think that the people of this country want to see an influx of disease from anywhere else,” the prime minister told reporters during a campaign visit to Hartlepool. “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.”

The government will have the right to rapidly remove countries from the green or amber lists if cases spiral quickly, but more routinely countries will be added to a “watch list”, raising questions about the implications for cancellations and insurance.

Portugal, Malta and Gibraltar are likely to be green list countries, where testing will be required before travel but not quarantine after returning. Popular destinations like Spain and France are expected to be on the amber list initially where home quarantine is still required. Red list countries, which are likely to include Brazil, UAE and South Africa, require quarantine in government-mandated hotels.

Advice to UK ministers will be given by the Joint Biosecurity Centre, which will give its final verdict on Wednesday, meaning an announcement is likely to be delayed until Friday because of local elections on Thursday. However, one government source said there was a possibility Johnson could make the announcement on Wednesday, a vital morale boost before the polls after a week battling stories of Tory sleaze.

The government will give the go-ahead for international travel to recommence on 17 May, and official advice to “minimise travel” will change to “travel safely, plan ahead” with no advice on limiting travel around the UK.

The Labour leader, Keir Starmer, warned there should not be a repeat of the “chopping and changing” of the travel corridors list introduced last summer. “We need to be very careful. I think it’s clear that the virus is increasing in some countries around the world, so we have to be very, very careful,” he told reporters during a campaign visit to Lewisham.

Agreement on opening of European borders is due to be sought from EU member states during meetings on Tuesday and Wednesday.

The existing requirement to undergo Covid testing before or after arrival or to quarantine could still be enforced by member states but EU officials hope there will be a gradual phasing out of these conditions.

Under the commission’s proposals, member states would allow travel into the EU of those people who had received, at least 14 days before arrival, the final dose of an authorised vaccine.

Even those who have not been fully vaccinated, which is likely to be a younger demographic in the UK, will be allowed into the EU if they are coming from a country with a “good epidemiological situation”.

As it stands, only seven countries worldwide are on a green list allowing for non-essential travel. The commission is proposing to increase the threshold of 14-day cumulative Covid-19 case notification rate from 25 to 100. The UK’s rate is about 23.2 per 100,000 people.

A senior official said the UK could be added to the green list but that it would depend on a reciprocal willingness to open its borders to all EU citizens. “The figures for the UK are good,” the EU official said. “Those vaccinated in the UK will be eligible to travel to the EU but [we are] mindful of other aspects: reciprocity. It is still a principle under this new recommendation.”

The commission is proposing, however, an emergency brake. When the epidemiological situation of a non-EU country worsens quickly and in particular if a variant of concern or interest is detected, a member state will be able to “urgently and temporarily suspend all inbound travel by non-EU citizens resident in such a country”.

Johnson also confirmed that the UK is likely to relax social distancing measures on 21 June when the government intends to loosen all remaining restrictions on hospitality and social gatherings. However, it is likely to mean that masks remain mandatory in some indoor settings.

“I think we have got a good chance of being able to dispense with the one-metre plus from 21 June,” Johnson said. “That is still dependent on the data, we can’t say it categorically yet, we have got to look at the epidemiology as we progress, we have got to look at where we get to with the disease. But that’s what it feels like to me right now.”

On Monday, the UK recorded 1,649 new coronavirus cases and just one death within 28 days of a positive Covid test, the lowest figure since 30 August last year. However, there is always a lag in reporting deaths – greater at weekends and bank holidays – so it does not necessarily mean only one such death has occurred the previous 24 hours.