The detail of how employers will be required to contribute a share of this from 1st August to October hasn't been released yet.
The media is reporting this badly - Rishi Sunak said:
Until the end of July, there will be no changes to the scheme whatsoever
From August to October the scheme will continue, for all sectors and regions of the UK, but with greater flexibility to support the transition back to work.
Employers currently using the scheme will be able to bring furloughed employees back part-time
We will ask employers to start sharing, with the government, the costs of paying people’s salaries
Workers will, through the combined efforts of government and employers, continue to receive the same level of support as they do now, at 80% of their salary, up to £2,500
He's not saying the government will continue to pay 80% of your salary.
He's saying that if employers furlough staff between July & October, those workers must be paid 80% of their salary - but THE EMPLOYER will be responsible for topping up whatever the difference is between what they can claim from government and the employees salary.
Lots will simply mandate people come back to work or make them redundant.