The Labour leader Sir Keir Starmer has reiterated calls for a so-called national 'circuit breaker' lockdown.
Speaking to ITV News Meridian political correspondent Phil Hornby, he said that although cases are comparatively low in the south east, infection rates are going up everywhere - and a circuit breaker would be the only way to avoid long lasting restrictions.
Meanwhile on Brexit he said the prospect of no deal was a "failure", while on the ongoing crisis in channel crossings he said we needed to act "in a humane way to desperate people" but said the solution would be international.
"If we don't take action....people will say 'how did you let this happen?'"
Starmer first announced his support following the release of papers from the government's science committee, SAGE, which indicated that a 'circuit breaker' could be an effective way to get on top of rising case numbers.
But he said he understood the "anxiety" that the south east would be unfairly restricted, given cases are much lower compared to the north of England.
"But if we don't take action, and in two or three months the south east is in restrictions that goes on for months on end, I think people might well look round to people like me and the prime minister and say 'How on earth did you let this happen?'"
He said should be time limited, but would not say whether he would end a lockdown after two or three weeks, regardless of the rate of cases.
He added that tying the lockdown to school holidays would "give us the best chance to break the cycle and get the virus under control."
"At the same time, we need to fix test and trace," the Labour leader said.
"There are thousands of people in the south east who should be self isolating are walking around not knowing.
"That isn't helping anyone."
No deal is a "failure"
On the prospect of the UK leaving the EU without a deal at the end of the transition period, Starmer said no deal is a "failure".
He said that people living in Kent would be "concerned" and "frustrated".
"[The Prime Minister] said he had an 'oven-ready' deal and he needs to deliver on that," he said.
Channel crossings need "humane" response
The Labour leader also address the ongoing challenge of migrants crossing the channel, reaching the shores of Kent and Sussex in small boats.
The government has said it will take a tough stance on the criminal gangs they say are responsible for the flow of people
Sir Keir said we need to "act in a humane way in relation to desperate people."
"But we do need to work with France and other neighbouring countries to manage and deal with this problem and we're not doing that."