Keir Starmer has accused Boris Johnson of “burying his head in the sand” over the mounting Covid crisis.
He says the PM failed to order a lockdown when it was needed and asks: “Where has Boris been?”
At least 20,000 lives are estimated to have been lost because the last lockdown in March was delayed by a week.
The Labour leader, who backed the call for a two-week “circuit-breaker” to break the spread of the virus claims Johnson refused to listen.
“He buried his head in the sand. He was not strong enough to stand up against his own party.”
Tory MPs have resisted calls for tougher restrictions, claiming it is unnecessary and economically too damaging.
Sir Keir slammed the PM for dismissing the science and for the fact that news of the news shutdown became known only through leaks to newspapers.
“That isn’t leadership. And it’s no way to run a country,” he said.
"The last thing we need is days before restrictions come in," he told reporters. "If they're necessary, they're necessary now.
"This lockdown is going on to at least December 2, everybody's seen the figures, and, therefore, I don't think it's fair to pretend that Christmas is going to be normal in any sense of the word.
"I think we need to level with the public on that."
The attacks came as members of the Independent Sage group of scientists, the non-Government group which shadows the official body, warned that a new lockdown might only just be in time to save Christmas.
Christina Pagel, of UCL and a member of the group, said: “Covid is moving faster than the political decision-making. The longer they’ve taken to decide on tighter measures the worse it is going to be.”
The scale of the crisis now is the result of a “wasted summer” said Sir Keir and the responsibility of “a Prime Minister who is in office but unable to lead”.
He called for a clear strategy “ cause ultimately it is the British people who will pay the price of his failures”.
“In the middle of this pandemic, the country is crying out for leadership that only a united party can provide”.