England's regional Covid tier system may need to be "strengthened" to get the country "through the winter", a senior government adviser has said.
Public Health England's Dr Susan Hopkins said they needed to look at what "tiers there may be in the future" when the lockdown ends on 2 December.
A three-tier system was used in England to tackle the spread of coronavirus before the national lockdown began.
Matt Hancock said the government hoped to bring back the regional tiers.
It comes as the UK announced another 21,363 daily Covid cases, as well as a further 213 deaths within 28 days of a positive test.
Speaking at the government's evening coronavirus briefing, Dr Hopkins, who is also a member of the government's scientific advisory group (Sage), said the "key" to knowing if the four-week lockdown in England was working was "if cases fall" and they expect to know that "in the next week".
"As long as we see cases decline we can make judgments... about opening up," she said.
She added that, prior to the lockdown, the "tiering of the country" had had a "different effect in each area".
"Tier three plus" had led to a reduction in cases in the North West, she said, while tier two "holds in some areas and not in others", depending on "how well individuals are taking that advice in".
However, she added: "We see very little effect from tier one and when we look at what tiers may be there in the future, we will have to think about strengthening them to get us through the winter months until the vaccine is available for everyone."
The government is adamant that it wants England's lockdown to end on 2 December.
But what replaces it is still very much a live discussion in the corridors of power.
There was always a question mark about how much infections would fall during the lockdown.
And clearly the impact has been undermined by the spike in cases last week when the daily number jumped by 10,000 to over 33,000 on Thursday.
That rise has been linked to a last bout of socialising before the lockdown came in.
The hope is cases will start falling this week.
But it will take much longer for that to filter through into fewer hospital cases - hence the suggestion that the regional tiers may need to be strengthened when lockdown ends.
One idea is to create a new tier four, which would see much tighter restrictions on hospitality opening.
But do not expect an announcement soon. Ministers will want to see exactly what happens to cases over the rest of the month.
Also speaking at the government's coronavirus briefing, Mr Hancock, the health secretary, said it was too early to know the impact of the second lockdown in England, which began on 5 November.
"At the moment, most of the tests we're getting back, and most of the positive cases, are from around the time the lockdown came in, so we are yet to see in the data - and it's too early to expect to see in the data - the impact of the second lockdown," he said.
"But we absolutely hope to be able to replace the national lockdown with a tiered system similar to what we had before."
At a briefing on Monday, the prime minister's official spokesman said: "We are committed to setting out next week what the replacement regime will be and that will be a return to the localised approach and we're actively working on those plans at the moment."
Mr Hancock also confirmed:
- The UK has secured five million doses of the new Moderna vaccine - which has shown in early data that it is nearly 95% effective in protecting against Covid-19. Mr Hancock said that if it was found to be safe, it would be available in the UK in spring next year
- The NHS will be opening a network of 40 "long Covid" clinics across England, which will be in place by the end of the month
- Two new "mega labs" will open early next year and add another 600,000 to the UK's testing capacity - doubling the current testing capacity
Before England went into its second lockdown, nearly a fifth of the population was living in tier three areas - those under the toughest coronavirus restrictions. They included those in West Yorkshire, South Yorkshire, Greater Manchester, Lancashire, the Liverpool City Region, Warrington and Nottinghamshire.