Boris Johnson has refused to predict the scale of job losses facing the UK but he warned workers are at “very, very serious” risk.

The Prime Minister defended his plans to boost the economy amid the Covid-19 pandemic before saying of Labour: “We’re the builders, they’re the blockers. We’re the doers, they’re the ditherers.”

His counter attack came after Labour leader Sir Keir Starmer warned the PM is “blind to the risks” of easing lockdown restrictions in England and trying to “brush away” concerns raised by the Opposition.

Sir Keir also said Chancellor Rishi Sunak’s financial statement next week could be the “last chance to save millions of jobs”, as he pressed for the furlough scheme to be extended to at-risk areas of the economy.

Speaking at Prime Minister’s Questions, Sir Keir said there is nationwide lifting of lockdown restrictions this weekend “without an app, without clear data for local authorities or the world-beating system we were promised”.

He added: “I support the easing of restrictions but unlike the Prime Minister, I’m not blind to the risks and I don’t think anybody else should be.

“Of the 22,000 new cases of Covid infections per week in mid-June, just 5,000 were reached and asked to provide details.

“So now three-quarters of people with Covid-19 are not being reached. How does the Prime Minister explain that?”

Mr Johnson replied: “As he knows very well, the test, track and trace operation is actually reaching huge numbers of people and causing them to self-isolate in ways I don’t think he conceivably could have expected a month ago when this system was set up.”

I'm not going to give a figure for the number of job losses that may or may not take place but of course the risk is very, very serious

Mr Johnson added the test and trace system has reached “113,000 contacts who have undertaken to self-isolate to stop the disease spreading”.

But Sir Keir warned there is a “real gap in the system”, telling the PM: “You can’t just brush it away by referencing those who are contacted. It’s a real problem and it’s growing, and it’s going to have to be addressed.

“The Prime Minister did this at phase one, brushing away serious concerns.”

Sir Keir said that amid Mr Johnson’s “normal bluster”, his speech on Tuesday contained a “striking line” about jobs not coming back for people, adding: “I fear this is the equivalent line to the line in the Prime Minister’s speech on March 12 when he said ‘I must level with you, many more families are going to lose loved ones before their time’, and we know what happened next.”

He called for a “laser-like focus” on protecting jobs, asking: “So how many jobs does the Prime Minister think yesterday’s announcement will protect?”

Mr Johnson claimed the Government has protected 11 million jobs in the crisis, adding: “I’m not going to give a figure for the number of job losses that may or may not take place but of course the risk is very, very serious, as he rightly says.”

The PM defended the Government’s spending plans, adding: “We’re going to build, build, build and deliver jobs, jobs, jobs for the people of this country.”

Sir Keir then highlighted recent job losses at Airbus, easyJet and others, adding: “Next week’s financial statement could be the last chance to save millions of jobs.

“Will the Prime Minister start now by extending the furlough scheme for those parts of the economy which are still most at risk?”

Mr Johnson said the best thing to do is help return the economy to health by ensuring people are back in work and the virus is “defeated and under control”, adding Labour could “stop equivocating, doing one thing one week and one thing another week”.

Mr Johnson also claimed Labour is being “bossed around” by the unions on returning children to school.

He added: “We’re the builders, they’re the blockers. We’re the doers, they’re the ditherers. We’re going to get on with it and take this country forward.”