Britain partially reopened schools on Monday and allowed the most vulnerable to venture outdoors despite warnings that the world's second worst-hit country is moving too quickly out of its coronavirus lockdown.

A death toll that now officially stands at 38,489 has piled political pressure on Prime Minister Boris Johnson, who was elected in December with a big majority.

Johnson spent much of the past week stamping out a scandal sparked by his chief adviser's decision to drive to a picturesque castle with his family while everyone was under orders to limit outdoor exercise to an hour a day.

Dozens of members of Johnson's own party joined a failed effort by the opposition to get Dominic Cummings fired for undermining the government's public message on health. The furore over Cummings appears to have abated but concern about Johnson's handling of the crisis remains.

His public support has suffered the sharpest fall for a Conservative party leader in 10 years -- nine points in a YouGov poll and 21 points in a survey for the Daily Mail.

'Spreading too fast'

Yet the mood in Britain is clearly improving as the number of daily deaths drops. Parks and beaches have been filled for two successive weekends in what has been one of the driest springs in over 100 years. Johnson has set out a timeline that allows two million younger children to return to school on Monday and older ones on June 15.

However, a survey conducted by the National Foundation for Educational Research found that primary school leaders expect 47 percent of families to keep their children home. The government is also allowing those most at risk of suffering serious consequences from the virus to spend time outdoors for the first time in two months.

"I do not underestimate just how difficult it has been for you," Johnson told the 2.2 million Britons who fall into the extreme risk category.

The UK government has also been encouraged by the positive experience of other European countries that have started to return to something resembling the old way of life. But critics argue that the so-called R rate of transmission -- estimated nationally at between 0.7 and 0.9 -- was still dangerously close to the 1.0 figure above which the virus's spread grows.

The R rate estimates the number of people one infected person passes the virus to. Several members of the government's scientific advisory group have warned that restrictions were being lifted prematurely. "COVID-19 spreading too fast to lift lockdown in England," scientific advisor Jeremy Farrar said on Twitter.

Minister Alok Sharma told the BBC on Monday that the "scientific advice does differ" but that the overall view from the official body advising the government was that "we must do this cautiousy". The group has more than 50 members and disagreements are to be expected -- although public criticism of the government's policies from its own advisers is relatively rare. "These are very cautious steps we are taking," added Sharma.

Hurting the poor

The scientists are not the only ones to express concern. National Education Union co-leader Mary Bousted said the government has had to revise its school reopening guidance 41 times since mid-May.

There were "things they had forgotten, things they didn't know, and things they got wrong (and that) had to be added in", Bousted told Sky News. The schools will only start reopening in England because each of Britain's four nations follows its own health guidelines.

Scotland is waiting until August and Northern Ireland is eyeing September, while Wales is still making up its mind. Communities minister Robert Jenrick said a return to school was essential because a lack of classes and lunch provision was hitting disadvantaged families especially hard.

"All of the evidence suggests that it is children from the most deprived, the poorer households who are losing out," Jenrick said Sunday. "I don't want that to continue."