The government's ability to test people for coronavirus has been "inadequate" throughout the pandemic, a committee of MPs has said.
The Science and Technology Committee said capacity had not been increased "early or boldly enough".
It said a lack of capacity had driven initial decisions in mid-March to scale back contact tracing and largely restrict tests to hospital patients.
No 10 said testing had since been expanded on "an unprecedented scale".
Committee chairman Greg Clark said ministers would need to "apply the lessons" from the "slowness" of increases to testing to other areas.
In a letter to Prime Minister Boris Johnson, the Conservative MP added that capacity "drove strategy, rather than strategy driving capacity".
But Work and Pensions Secretary Therese Coffey said the government could look on the ramp up of testing capacity "with pride".
The UK significantly increased its testing capacity throughout April, although it has previously faced criticism it was initially too slow to do so.
A target for 100,000 daily tests was initially met on 1 May, but then missed for eight consecutive days after that before being met again on 10 May.
On Monday, after 100,678 tests were provided in the previous 24 hours, ministers announced another expansion in eligibility, with everyone aged five and over now able to get tested if they show symptoms.
Increasing testing capacity has also been seen as crucial in allowing a mass programme to track infected people using an NHS app, which ministers want to launch UK-wide "in the coming weeks".
In his letter, Mr Clark laid out several recommendations to ministers.
He accused Public Health England (PHE) of initially opting to "concentrate" tests in a limited number of its own laboratories and only expanding capacity "gradually".
He said that had led to the decision to initially abandon contact-tracing as a strategy on 12 March, and meant care home residents could not be tested when the virus was spreading at its fastest rate.
He added that evidence taken by his committee from experts in South Korea, Hong Kong and Germany had shown the need for mass testing was "identifiable from the beginning".
Mr Clark told BBC News: "There are going to be mistakes made as we are operating in a fog on uncertainty, and they will be made by ministers, by officials and by scientists.
"The crucial thing now is there will be decisions to be taken in the weeks and months ahead - for example, the roll-out of antibody tests and we hope a vaccine - and we have to be able to learn the lessons so far."
PHE defends role
In response to the letter, PHE said it was "not responsible" for the UK's testing strategy, which "has been led by the Department of Health and Social Care".
Its chief executive Duncan Selbie added that "any testing facility with the right technology and containment" could conduct the test it approved after security restrictions were lowered on 3 March.
"PHE did not constrain or seek to control any laboratory either public, university or commercial from conducting testing," he added.
Ms Coffey said she recognised there was "little capacity" for testing at the beginning of the outbreak as it was "solely based" on the PHE's reach.
But she told BBC Breakfast: "From pretty much a standing start... to get to a capacity and actual tests being done of 100,000 within about six weeks, I think is pretty full-on and actually I think something we can look on with pride."
'Unprecedented' testing increase
The committee also said the transparency of scientific advice to ministers needed to be improved, and called for summaries of advice to be published "now and regularly".
It added that while some scientific papers discussed by the Scientific Advisory Group for Emergencies (Sage) had been published, 92 out of the current total of 120 had yet to be made public.
A statement from Downing Street said that testing rates had increased "on an unprecedented scale" from 2,000 per day at the start of March to more than 100,000 in May.
"Now everyone aged five and over who has symptoms and needs a test can get one - and we will continue to build this capacity," it added.
"This is an unprecedented global pandemic and we have taken the right steps at the right time to combat it, guided at all times by the best scientific advice."
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