Health expert Professor Chris Whitty has said he cannot see a system of local lockdowns returning.
But he had warned that the emergence of a variant which was able to have "unconstrained growth" could mean an "alarm cord" must be pulled.
The top medic made the comments while addressing a wide range of questions about the pandemic during a Royal Society of Medicine webinar.
As for the long term, Prof Whitty repeated his assertion that coronavirus "is not going to go away", and said the future will be about working out how to "minimise mortality whilst not maximising the economic and particularly social impacts on our fellow citizens".
The chief medical officer for England said: "The only area where I think we technically are going to have to pull the alarm cord is if a variant of concern comes in that we can see is now back to a situation it could manage unconstrained growth, because the immunological response to it is just not there."
He was also hopeful that a "wide portfolio" of coronavirus vaccines could be available in two years but a cautious approach is needed in the meantime.
While he said technology and the ability to tailor vaccines to new variants will eventually "find a way through", there remains a level of risk before then.
Prof Whitty said the approach is cautious "because we've got such a difficult situation to go through at the moment".
But he added: "I don't think though this should be seen as an indefinite posture, I think this is a matter of probably the next year or two whilst we understand how to do this and find a way of responding rapidly to variants."
He said if we "scroll forward two years I think we're going to have a very wide portfolio of vaccines".
Technology can "turn around a vaccine to a new variant incredibly fast, compared to how historically we've been able to do it", he said.
He added: "So I think technology will find a way through this in the long run, but we've got a period of risk between now and then."
The idea that it is possible to stop any variants of the virus being imported to the UK is "not a realistic starting point", he said.
He told the webinar: "Anybody who believes that they can actually just put up some border policy or some overall policy that stops the possibility (of variants) is misunderstanding the problem completely."
He said while R is less than 1, variants coming in "don't have much of a foothold", but he added that R is anticipated to rise above 1 as more things open up in the lockdown exit road map.
In Wales, First Minister Mark Drakeford has said that if coronavirus figures continue to fall, people in Wales could be limited to just three restrictions by the end of the year.
He has warned that some restrictions will remain throughout 2021 and has repeatedly expressed his concern that another wave of coronavirus is already "baked in" and cannot be avoided.
