General Sir Gordon Messenger said coronavirus screening people without symptoms may not be possible everywhere “at the same time”.
He said planning was “still very much underway” for the 23 million people entering level 3, but the capacities would “be sequenced in time.”
Community testing – using tests that give a result in less than 30 minutes – is credited as allowing Liverpool to enter this week’s new regime at Level 2.
Boris Johnson has said expanding the system across England is vital in reducing infection rates and allowing areas to move on to looser restrictions.
Speaking alongside the health secretary at No 10, Sir Gordon said he was unsure how many people mass tests would reach to be with.
He said that “would vary from region to region and region to region”.
“We are aware of the possibility that we will not be able to do all of this all at once, but we feel that local authorities are at different levels of readiness and availability to do it”, he added. .
“And therefore, I can see this as an offering that will flow over time and into January and beyond.
“The priority we give, the levels of support we give, will be based on the infection rate, how long these areas have been under severe restrictions, how mature their plans are, how prepared they are. ”
Sir Gordon said the “pioneers” in terms of being able to participate in the testing program would be identified within the next week.
The military will also not be able to help implement community testing in all areas, he added.
Around 2,000 troops have helped with the Liverpool program, but such support will now be targeted.
“I can say with confidence that this cannot be replicated across the country, and therefore military support, as well as all other types of central support, must be targeted where it is most needed and where it is needed. may have the greatest effect, ”said Sir Gordon.
He said testing programs would be “delivered locally with considerable support from the center.”
Matt Hancock said local authorities could get funding of up to £ 14 for each test performed – as he used briefing number 10 to declare the pandemic was “Back under control”.
Respected study found infections dropped almost a third in England’s last lockdown, with the biggest improvement in the North.
The React study of more than 105,000 volunteers estimated that one in 100 people in England had the virus between November 13 and 24, down from the 1 in 80 reported on November 2.
Level 3 councils will be able to apply for a six-week testing program to try to identify asymptomatic people, the health and welfare ministry said.
However, concerns about the accuracy of lateral flow tests used for community testing prompted Sheffield Council to warn nursing homes not to use them.