Greater Manchester hospital intensive care beds will be overwhelmed with coronavirus patients by November 12 in a best-case scenario, Downing Street has claimed.

Hitting back at Andy Burnham’s claims that Boris Johnson was “exaggerating” the seriousness of infections in Manchester, No.10 outlined the latest data informing negotiations on the city entering a tier 3 local lockdown.

The prime minister’s official spokesperson said cases continue to rise in Greater Manchester, with infections among over-60s tripling in the most recent 15 days where full data is available.

Currently, the number of Covid-19 patients in intensive care in the city is around 40% of the number seen at the height of the first wave of the pandemic in spring.

Given hospitalisations occur two to three weeks after transmission, Downing Street expects that number to rise “significantly” over the next few weeks.

Under projections that assume hospitalisations double every 14 days – which the spokesperson said was a best-case scenario outlined by the government’s SPI-M scientific committee – all free intensive care capacity will be used by October 28.

Hospitalisations will go past the peak of the first wave by November 2, they predict, while Covid patients would take up the city’s entire intensive care capacity by November 8, and the entire surge capacity by November 12.

Surge capacity is built by local NHS managers freeing up space in hospitals.

But the figures do not take into account extra beds at Nightingale hospitals, including one in Manchester that is currently being prepared for potential reopening.

Asked if the projections meant hospitals being overwhelmed by November 12, the spokesperson said: “Yes, that’s the entire surge ICU capacity.”

It comes as Johnson and the Greater Manchester mayor are locked in a standoff over whether the city should enter “very high” coronavirus restrictions, with Burnham apparently holding out for more financial support.

The PM’s official spokesperson said the government has committed a total of £465m of extra funding for English local authorities on top of £300m for “test, trace and contain” work.

But on reports the government could offer Manchester £100m to get agreement to enter tier 3, the spokesperson said: “Certainly I wasn’t familiar with the sort of numbers that were around this morning.”

No.10 also appeared to reject Burnham’s call for a parliamentary debate and vote on support for workers and businesses hit by restrictions before areas go into tier 3, as a way to break the “impasse”.

But Johnson’s spokesperson said: “The chancellor set out his financial support package to parliament, including for areas moving to high alert levels, and since then the House of Commons has spent more than 11 hours debating the latest situation, which has included extensive debate on the financial support package.

“I think parliament has had and continues to have a lot of opportunity to debate the situation and the government’s response to it.”

Senior Conservatives, including the influential chair of the 1922 committee, Sir Graham Brady, have backed the Greater Manchester mayor in resisting tier 3 for the region.

Earlier, communities secretary Robert Jenrick said there had been “productive” negotiations with Greater Manchester but Monday’s talks would be the “final discussions”.

“We do now need to draw these conversations to a conclusion and to take decisive action,” Jenrick told BBC Radio 4’s Today programme.

Downing Street said discussions about coronavirus restrictions were also taking place with leaders from the north-east, South Yorkshire, West Yorkshire and Nottinghamshire.

Liverpool City Region received a £44m package as part of its Tier 3 measures, but Greater Manchester wants more extensive support – including a furlough scheme paying 80% of wages for affected workers.

Responding, No.10 again pointed to figures showing that workers can access 67% of their wages on chancellor Rishi Sunak’s job support scheme, and in some cases top up some of the remaining lost earnings through universal credit (UC) to a level which could reach at most 88% of their original income.

But many will receive significantly less than that figure due to the way UC works.

Burnham said whether a deal can be reached is “not about the size of the cheque”.

He told Sky News: “It’s about protecting low-paid workers, people who are self-employed, supporting businesses and preventing them from collapsing. That’s what this is about.

“We’ve always said we would put people’s health first, and we will do that. But health is about more than controlling the virus – people’s mental health, I think, is now pretty low given that we’ve been under restrictions here for three months already.”

The row comes as the Welsh government introduces a two-week “circuit breaker” lockdown similar to the first restrictions imposed in March, covering the half-term break (October 23 to November 2).

Scotland and Northern Ireland have both imposed their own versions of a “circuit breaker”, with pressure mounting on England to U-turn and do the same.