There is still "nothing in the data" to say the June 21 lockdown easing shouldn't go ahead, Downing Street said today - despite mounting fears about new strains in the UK.
Boris Johnson's official spokesman said there is "currently" no data that suggests step four of the PM's lockdown roadmap will be blown off course.
But he added data that emerges this week about the Delta ('Indian') variant will be "crucial" - just seven days before the PM announces a red or green light for unlocking.
It comes after headlines last week about a so-called 'Nepal variant' of the virus. Health officials later clarified it was in fact not a full-blown variant, but a "spike mutation of interest" on the existing Delta strain.
Downing Street today said there had been 23 cases of the spike protein mutation identified in the UK up to June 3.
Health Secretary Matt Hancock is due to update the House of Commons at 3.30pm.
Step four of the roadmap involves removing the six-person limit on indoor gatherings and allows nightclubs to open.
Sir David King, who was Chief Scientific Adviser from 2000 to 2007 and who chairs the Independent Sage Group, said today that the UK is seeing "evidence" of the third wave.
But the Prime Minister's official spokesman said: "There still remains that there is nothing in the data currently to suggest Step 4 can't go ahead at the earliest date.
"But we do need to look very closely at the data over this coming week, which will be crucial to decide and really to get a sense of the data, particularly on hospitalisations and whether or not the excellent vaccine rollout programme has sufficiently severed that link between the increase in cases, which we always expected to happen, particularly after Step 3, and that subsequently leading to hospitalisations and deaths."
Asked if there is evidence of a third wave, the spokesman said: "We can see that the cases are rising in the UK, that is both due to the increased transmissibility of the Delta variant, and to a certain extent the opening up of measures taken in Step 3."
Scientists are split over the scale of England's rising case rates as school pupils return from their half term break today.
Health Secretary Matt Hancock yesterday warned the government was prepared to delay the June 21 unlocking if necessary.
Advice on face masks, social distancing and working from home could remain after June 21 even if other easings go ahead, it is reported today.
And Health Minister Lord Bethell indicated twice-a-week testing for school pupils will last until at least the summer holidays, possibly longer.
Writing in the Telegraph, he said making the tests part of an “everyday routine” can “underpin the reopening of other things we all love.”
He added: “Fifty million tests have got us here; here's to 50 million more. Let's not lose what's been achieved so far.”
Some 33,496 people have tested positive for Covid in the UK in the latest seven days - up 49% in a week.
But the number of patients admitted to hospital was 869, down 0.3% on the week before.
Solicitor General Lucy Frazer told LBC: "What we know at the moment is that the infection rate is rising, but that’s not seeping out in hospitalisations at the rate that it did in the other lockdowns.
"So we are seeing a flat lining of hospitalisations and the reason for that is, the reason you were identifying earlier on your programme, that the vaccination programme has been so successful."
