Rishi Sunak will use the daily Downing Street press conference to outline changes to the job retention scheme, which has so far covered the wages of 8.4 million staff unable to work during lockdown - costing £15 billion.
Ministers have said they will extend the scheme covering 80% of workers' salaries up to £2,500 per month until the end of October, with employers expected to make a contribution.
Treasury sources did not deny reports that the Chancellor will ask employers to contribute around 20% of wages, as well as National Insurance and pension contributions from August.
Meanwhile Mr Sunak is facing calls, including from a cross-party group of 113 MPs, to extend the scheme supporting self-employed workers past Sunday or risk leaving many "without work and without support".
It comes after Boris Johnson announced a gradual easing of the lockdown in England, with friends and families able to meet in parks and gardens in socially distanced groups of six from Monday.
The Prime Minister said all five of his tests to move into the next phase had been met, allowing schools to begin reopening and greater contact to be permitted from Monday.
Mr Johnson on Thursday confirmed people will be able to see "both parents at once, or both grandparents at once", in what he said will be a "long-awaited and joyful moment" for many.
But the PM continues to be dogged by questions over his top aide Dominic Cummings after Durham police said he may have committed "a minor breach" of lockdown rules.
In Scotland, a gradual relaxation of lockdown begins on Friday with a similar plan to allow outside gatherings, though First Minister Nicola Sturgeon is permitting groups of up to eight people.
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