All four of the UK’s chief medical officers rejected suggestions from No 10 that the coronavirus threat level could be reduced because it contradicted evidence that showed the virus was still widespread, the Guardian has been told. A senior source in one devolved government said the chief medical officers of England, Scotland, Wales and Northern Ireland discussed and refused Boris Johnson’s proposal. It comes after Downing Street confirmed that the decision for England’s coronavirus alert level to remain at four – despite this week’s easing of some lockdown restrictions – was made by England’s CMO, Prof Chris Whitty, indicating he vetoed the UK government’s wish for it to be lowered. The senior source also said that despite the CMOs rejecting lowering the threat level, Johnson floated the idea in a teleconference later the same day with the first ministers of Scotland, Wales and Northern Ireland. The first ministers also resisted the move, telling the prime minister that it went against the CMOs’ advice. A source in another devolved government said the CMOs had been in consistent “lock step” on what should be done throughout the crisis. A source said: “My understanding is that the sequence of events is there was a CMO call on the same day there was an FMs [first ministers] call with the prime minister, which was arranged at short notice. The CMOs had been absolutely of one mind that the [infection] numbers didn’t justify reducing the coronavirus threat level at all. “But at least one point he [Johnson] seemed to be trying to test the water with the devolved administrations as to whether the level should be dropped and was told, pretty much directly, no, because the CMOs had said no.” Johnson’s spokesman confirmed that Whitty’s decision to keep England’s threat level at four was guided by data provided by the government’s new Joint Biosecurity Centre (JBC). The news came as Downing Street announced it was winding down its programme of coronavirus press conferences from every day to five a week, with those on Saturday and Sunday scrapped. “In terms of the weekends, it is just a fact that the numbers who are viewing at weekends do tend to be significantly lower,” Johnson’s spokesman said. The prime minister would lead one press conference a week, he added. The government’s formal roadmap for emerging from coronavirus restrictions, published last month, gave a different rationale, stating: “The JBC will be responsible for setting the new Covid-19 alert level to communicate the current level of risk clearly to the public.” The expectation had been that by the time Monday’s loosened rules came into force, with more businesses opening and groups of up to six people allowed to meet outside, the five-point alert system would have been reduced from four, which means coronavirus transmission “is high or rising exponentially”, to three, where the virus is only “in general circulation”. However, the level stayed the same, with ministers saying it was “transitioning from level four to level three”. This prompted speculation that the JBC, set up to help guide the UK out of lockdown, had blocked the change. This in turn caused some confusion as to whether the JBC was even yet operational, and thus how it could have made the decision. Asked about this, Johnson’s spokesman said: “The Joint Biosecurity Centre has begun operating. It’s reporting to a director general based in the Department for Health and Social Care. It has a data and analysis team which is analysing the data on coronavirus to inform the alert level, and the testing scheme. “In terms of the setting of the alert level, it’s ultimately for the chief medical officers, who are informed by the data which has been collected, collated and analysed by the JBC.” Asked whether this meant Whitty had decided the level must remain at four, the spokesman said: “There are the four chief medical officers, but Chris Whitty is the chief medical officer for England.” Questioned whether the relaxation of lockdown rules in effect went against Whitty’s judgment, the spokesman said: “I don’t accept that. With the decisions in terms of the easements we made yesterday, I’ll stress again how cautious they were, and how we’re moving forwards at a very gradual rate. Secondly, they were based upon us meeting the five tests, and that is what we are currently doing.” The roadmap also set out five tests for easing restrictions, covering areas such as infection rates, testing capacity and the impact on the NHS. The spokesman added: “The very gradual changes that we made yesterday were guided by the scientific and medical advice.”