“Social bubbles” allowing people to mix with a fixed small group of family and friends could be a part of easing the lockdown, Downing Street has hinted, but experts warned that tougher isolation and quarantining measures may be needed at the same time as any relaxation of restrictions.

Boris Johnson’s official spokesman signalled No 10 was open to the idea on Wednesday, saying it was “very alive to the issue of social isolation and the need for mental wellbeing”.

His comments reflected the priority the government is putting on trying to find a way for people to see close family, believing that is the aspect of the lockdown that people are finding toughest.

Under the social bubble proposal, people would be allowed to combine their household with one or two others, up to a maximum of 10 people. A cautious version of the plan would probably mean that the vulnerable such as the over-70s and those with underlying health conditions would be advised to keep isolating and not merge with other households.

However, experts are concerned that the government needs to more rigorously quarantine new cases of coronavirus at the point that it moves to the “test, track and isolate” phase advocated by the World Health Organization (WHO).

Ministers have already conceded the need for mass testing and an army of contact tracers, after abandoning that strategy of containment early in the epidemic. They now talk about the need for “a test, track and trace” policy.

But critics said they are making a mistake by failing to talk about a tougher isolation response, which in some other countries involves a longer, 14-day period of quarantining for confirmed cases and asking some to quarantine in state facilities. China has even made forcible quarantining mandatory, although that is unlikely to occur in the UK.

Jeremy Hunt, the chair of the health select committee and a former health secretary, told the Guardian: “The key point about the success [of] South Korea and Taiwan is that it was as much a quarantining strategy as it was a contact tracing strategy, with the object to take out of circulation anyone who has Covid or is likely to have Covid.”

At No 10’s daily press briefing, Dominic Raab, the foreign secretary, and Yvonne Doyle of Public Health England suggested the government could look at relocating care home residents sick with coronavirus to the largely empty Nightingale hospitals as part of the strategy to bolster quarantining in the future. However, they said it would have to be done carefully and was only one of the options under review.

The UK may also consider asking those with confirmed coronavirus to quarantine for longer than the seven days currently required.

Speaking in the House of Lords, James Bethell, a health minister, signalled this was actively under review. “The question of isolation remains one for which we are reviewing our advice. We are in constant contact with other countries to learn more about best practice,” he said.

Paul Hunter, professor in medicine at the University of East Anglia, said the UK ought to require a 14-day period of isolation for those with symptoms, in line with the WHO. “At the moment it probably doesn’t matter a great deal, because we’re not trying to stop every transmission, but if we manage to get to the point where there are very low numbers in the community, letting people out before 14 days is a significant source of concern,” he said.

Under such circumstances, he said, more thought needs to be given to increasing compliance. “Once we’re back to small numbers we cannot afford to allow rogue citizens to do what they like. There are undoubtedly people in the UK who ignore guidance. Not many, but some. A person like that could ultimately be responsible for going into a care home and introducing the infection, causing 20-30 residents to die over the next month. We’ve got to take that seriously.”

Another expert, Devi Sridhar, the global public policy chair at the University of Edinburgh, said the government could consider recommending isolation outside the home if confirmed cases live with vulnerable people.

“‘Test, trace, isolate’ only works if each of those components are included,” she said. “There needs to be work in tandem across these three areas including on how incentives are created for people to isolate at home for 14 days or alternative housing arrangements if they live with elderly or vulnerable individuals.”

No 10 has repeatedly talked about the possibility that lockdown restrictions could be both loosened in some areas and tightened in other areas, as the government seeks a balance between returning to normal life and trying to avoid a second peak of the virus.

Priti Patel, the home secretary, signalled tougher quarantining requirements on new arrivals in the UK are also under consideration when she appeared before the home affairs committee on Wednesday.

Further restrictions could include asking people to wear face coverings in enclosed public places, which is already recommended in Scotland.

Social bubbles is one of the possible ways of easing restrictions, but other possibilities include letting some shops reopen, encouraging people to go back to work with staggered start times and social distancing, and reopening schools with smaller class sizes and different opening hours.

Asked on Wednesday whether the government was considering social bubbles, Johnson’s spokesman said: “We have said there’s extensive work going on in government to look at the next phase of the coronavirus response and also talked about how we could relax measures in some areas and toughen them in others. We are also very alive to the issue of social isolation and the need for mental wellbeing, as people help us to deal with the spread of this pandemic.

“But in terms of specific details, you will have to wait until such a time as we have full medical and scientific advice, and we’re ready to set out what happens next. We will have to take decisions based on the scientific evidence and guided by the fact we are not going to do anything which could lead to the virus being able to spread exponentially again.”

A Whitehall source told the Guardian that it was one of many options under consideration and not one of the most outlandish but “there are lots of details that would have to be worked out before it is workable”.