Sir Keir Starmer has said the UK's coronavirus testing regime is "all over the place" and claimed the Government has "effectively lost control".
The Labour leader told Sky News on Sunday that if he was prime minister, he would apologise for the testing crisis as he said the system is "near collapse".
He told Sky News: “I don’t think a national lockdown is inevitable, I think it’s more likely because testing is all over the place.
“But I’ve said to the Prime Minister you need to take swift action, decisive action. The infection rate is clearly going up.
“The testing regime is all over the place and I think one of the concerns I have, and a lot of people have, is that because the Government’s now effectively lost control of testing, it doesn’t necessarily know where the virus is.
“So if I was the prime minister, I would apologise for the fact that testing is all over the place and instead of using the summer to prepare for the autumn, which is what we said should happen.
"We’re in this position just when we need testing to be at its very best, it’s near collapse.”
Earlier, Sir Keir warned of a "flood" of school closures and urged Boris Johnson to put children "at the front of the queue" when it comes to testing.
He also called on Downing Street to entrust coronavirus testing to local authorities, who have a comprehensive understanding of their communities.
It comes after an Evening Standard investigation found that earlier this week test appointments were not available to book online in any of London's 32 boroughs.
Sir Keir told the Sunday Mirror that testing should not be run from London.
“They were up for this months ago but even at the eleventh hour I say localise this,” he said.
His deputy Angela Rayner called on the Prime Minister to “get his priorities right”, adding in the Mirror: “The British people deserve better.”
Sir Keir warned of a “flood” of school closures unless pupils were able to get the tests they needed.
His call came amid reports that 350 schools in England and Wales were forced to close completely or to send children home last week following positive Covid-19 tests.
Sir Keir said it was essential children whose schooling was disrupted by the lockdown did not lose out even more because a shortage of tests meant they were unable to return to the classroom.
“If the Prime Minister does not get a grip of the testing crisis, children will be robbed of an education. We are seeing a growing flood of schools closures,” he said.
He said the testing system was “not working” and did not address the “unique challenges” facing many families.
“That is why I’m urging the Prime Minister, like our key workers, to put children at the front of the queue for testing. To this week give parents a cast iron guarantee that they can get their child a test within 24 hours and the result back 24 hours later,” he said.
Meanwhile, Labour has joined the Scottish and Welsh governments in calling on the Prime Minister to summon a meeting of the Government’s Cobra civil contingencies committee, which has not met since May, to consider the worsening situation.
Sir Keir has offered to sit in on the meetings himself to help plan for the second wave of the virus and called for London Mayor Sadiq Khan and the First Ministers of Scotland and Wales to also be present, saying Mr Johnson “isn’t up to the job”.
This is the time for swift, decisive national action. We cannot afford to be too slow.
That’s why I’m asking the Prime Minister to convene a COBRA meeting and to update the country on the measures the Government‘s taking to keep the virus under control, including to fix testing.— Keir Starmer (@Keir_Starmer)September 18, 2020
“What people have seen for weeks and months is a pattern of refusing to acknowledge a problem exists, then doing a U-turn, and finally shifting the blame on to someone else,” he told the Mirror.
“I appreciate this is not easy and, if it was just a matter of one or two U-turns, that’s understandable. But he’s done 12. That’s serial incompetence.”
The Labour leader said Mr Johnson needed to act “swiftly and decisively now to get infections under control so that Christmas is not lost”.
His comments came at the start of Labour Connected – a four-day online event in place of the party’s annual conference, which was cancelled because of the pandemic.
Sir Keir is expected to use his keynote speech on Tuesday to set out his vision for Britain after Covid-19 and to explain how he intends to lead Labour back to power.
Mr Khan, who addresses the event on Sunday, will accuse the Government of having “catastrophically let down” the country through its serial incompetence, making another lockdown increasingly likely.
“These times called for a government that could put ideology, dogma and ego aside, and calmly and competently do whatever it took to save lives and jobs,” he is expected to say.
“Unfortunately, we got the exact opposite. Just when we required a steady, capable hand on the tiller, we’ve had a hapless government that keeps on steering us onto the rocks.”
Additional reporting by PA Media.