Chancellor Rishi Sunak has said it is "impossible" to predict how many jobs the government's new wage subsidy scheme will save. The scheme, set to replace furlough, will see the government top up the pay of people unable to work full time. It aims to stop mass job cuts after the government introduced new measures to tackle a rise in coronavirus cases. Mr Sunak said he hoped the plan would "benefit large numbers", but he could not say what job is "viable or not". Under the Job Support Scheme, if bosses bring back workers part time, the government will help top up their wages with employers to at least three quarters of their full time pay. It will begin on 1 November and last for six months. Mr Sunak described the scheme as a "radical new policy", designed "to help protect as many jobs as possible [and] keep people in part-time work rather than laying them off". However, he said it would only support "viable jobs" as opposed to jobs that exist because the government is continuing to subsidise the wages. "It's not for me to sit here and make pronouncements upon exactly what job is viable or not but what we do need to do is evolve our support now that we're through the acute phase of the crisis," Mr Sunak said at a press conference after the scheme was unveiled. "We obviously can't sustain the same level of things that we were doing at the beginning of this crisis." Nearly three million workers - or 12% of the UK's workforce - are currently on partial or full furlough leave, according to official figures. The current furlough scheme ends on 31 October. The government's contribution to workers' pay will fall sharply compared with the furlough scheme. Under furlough, it initially paid 80% of a monthly wage up to £2,500 - under the new scheme this will drop to 22%. "The primary goal of our economic policy remains unchanged - to support people's jobs - but the way we achieve that must evolve," Mr Sunak said. "I cannot save every business, I cannot save every job." The scheme will cost the government an estimated £300m a month. Companies who use it can also still claim the Job Retention Bonus, where the government pays £1,000 for every furloughed employee who comes back to work until at least the end of January. Mr Sunak said a similar scheme for the self-employed would be available.