Slumped on the sofa after another day of home schooling, many families will have longingly eyed adverts for getaways: sun, sandy beaches and glittering pools, a much-needed reward after a year in the shadow of the coronavirus pandemic.

But ministers are becoming increasingly concerned they may have to ask the British public to sacrifice their hopes of a break abroad this summer. On Thursday, Priti Patel became the latest cabinet minister to say it was too soon to book an overseas break; Matt Hancock has already announced he is going to Cornwall.

Officials are anxiously awaiting the results of studies on whether new Covid variants are resistant to the existing vaccines, millions of doses of which are being distributed across the UK, but they are not expected for several weeks.

Tough UK border measures that came into effect this week were initially planned to last a fortnight, but stricter enforcement is already under consideration, including obliging arrivals to pay to stay in “quarantine hotels” while they self-isolate.

There are growing fears in government that the prime minister, so reluctant to “cancel Christmas”, may have to tell the public to abandon hopes of a dose of foreign sunshine this summer. Several government sources told the Guardian they expected border measures would have to be tightened, and ministers are even discussing a total travel ban.

A Department of Health and Social Care source said: “Should things proceed as we hope – which is cases come down because of lockdown, the rollout of the vaccine continues at pace and starts to have an impact – the focus on borders would increase, and rightly.

“As the cases come down in the UK, it will become more and more important to make sure that we are not introducing any variants that could be, if not immune, more resistant [to the vaccines]. There’s nothing to say they would be at the moment. If that evidence comes to light, then obviously that’s when borders would become the real focus.”

Hancock, the health secretary, has stressed that reformulating the vaccines to cope with a resistant variant should be relatively straightforward – he has compared it to replacing the wing mirrors on a Range Rover – but the new jabs would still need to be approved by the medicines regulator, manufactured and delivered to millions of people. “With these new variants, we do need to be extremely cautious,” a No 10 source said.

Meanwhile, travel from the UK to a string of other countries remains banned, as scientists assess the risks of the Kent variant that spread rapidly from south-east England. The government’s approach to the UK’s borders is in sharp contrast to the first wave of the pandemic, when banning international travel seemed unthinkably draconian to Boris Johnson.

Tough initial restrictions on arrivals from Wuhan, 273 of whom who were sent into enforced quarantine, gave way to a free-for-all from 13 March, when scientific advice suggested the virus was already being transmitted domestically. Quarantine requirements were not introduced until 9 June.

Many experts inside and outside government now believe that not imposing border restrictions earlier was a mistake – perhaps one of the most serious mistakes of last year. Michael Head, a senior research fellow on global health at the University of Southampton, described the failure to introduce border curbs early on as “very much a missed opportunity”.

“Covid-19 transmission is driven by super-spreading events, this is where dispersion is important. A small number of people will contribute to most of the transmission. Thus, even if the actual numbers of cases coming from international travel are low, these can seed new outbreaks and contribute to onward transmission around the community,” he said.

The Labour MP Yvette Cooper, the chair of the home office select committee, has consistently pressed the government over the lack of border controls. “If we had our time back again, and were thinking about January, February and the measures that could have been brought in and would have made a difference in helping to limit the scale of the pandemic in the first wave, border measures clearly should have been part of dealing with the crisis,” she said.

“Other countries, including New Zealand, Australia, South Korea, they put in very strong quarantine arrangements right from the very beginning, and the UK didn’t do any of those things. And then it inexplicably lifted [the guidance it had eventually put in place] on 13 March.”

“There was then no testing, no self-isolation,” she added. “What actually happened during that period before lockdown was that 1 million people came back into the country with no tests. Other countries were doing the opposite. Everywhere else was bringing in stronger and stronger restrictions at the border, and the UK was removing restrictions at the border. The first wave was significantly worse, and developed faster, as a result of us not having those.”

Experts told the home affairs select committee, which published a report on border controls in August, anything from 1,000 to 10,000 Covid cases may have been imported into the UK during this period.

Patel staked her claim to be on the right side of history this week. In comments that subsequently leaked, the home secretary told the Conservative Friends of India group: “On ‘should we have closed our borders earlier?’ the answer is yes, I was an advocate [of] closing them last March.”

People with knowledge of the discussions last year corroborated Patel’s account – but claimed she had not pressed the point. “Priti was up for it. I’m not sure it was because of a strongly held epidemiological view or just because she heard ‘close the borders’ and liked the sound of it,” one senior Tory commented drily. Another said: “She didn’t really push it.”

The prime minister’s former chief aide Dominic Cummings was also in favour of a more robust border policy, according to one source – with Johnson, as well as transport secretary, Grant Shapps, more sceptical about the benefits. Others recall “pushback” from Dominic Raab’s Foreign Office.

Government insiders point out that their scientific advisers were not pressing for tighter controls on arrivals either. Published minutes show the Scientific Advisory Group for Emergencies (Sage) committee of experts estimated on 3 February that reducing imported infections by 50% might only delay the onset of the pandemic in the UK by about five days – too short a period to make a difference to the under-pressure NHS, they concluded.

By March, they believed thousands of cases had already arrived in the UK, and it was too late for action to be effective. The chief scientific adviser, Sir Patrick Vallance, said at a Downing Street press conference on 13 March, as border controls were lifted, that there were already probably “between 5,000 and 10,000 people infected”. Prof John Edmunds, of Sage, agrees with that, saying: “March was already way too late.”

At the time, ministers were also concerned about the impact of halting flights on freight and trade. When quarantine measures were eventually introduced in June, freight drivers were excluded. In the run-up to the restrictions being imposed, ministers were also subject to intensive lobbying from a “quash quarantine” campaign, involving travel companies and backbench Conservative MPs alarmed about the economic costs of the measure.

“It’s not like just closing the door; it’s like closing the door and also refusing all parcels and deliveries. It has implications on food security, freight, all sorts of things, so it’s not something you want to do lightly,” said one witness to last year’s agonising decision-making. But they added: “If you knew now what you knew then, you would have closed the borders.”

One harrowing year on, as the vaccine programme gathers speed but the UK has already mourned 100,000 Covid deaths, ministers appear determined not to make the same mistakes again – and that may mean sunshine breaks abroad will have to wait.