Education unions are meeting the chief medical officer and other experts on Friday over the Government’s push to reopen schools in England amid mounting criticism of the approach.

The unions and the Local Government Association (LGA) have expressed concerns as ministers push for a gradual reopening of classrooms from June 1.

But the teaching unions have faced their own backlash over their approach, with former Labour education secretary Lord Blunkett saying: “I am being deeply critical of the attitude.

“It’s about how can we work together to make it work as safely as possible. Anyone who works against that in my view is working against the interests of children.”

The schools debate came as Labour took aim at the Government’s track-and-trace plans – seen as key to allowing the UK to lift the most stringent lockdown measures – warning ministers its team of contact tracers should be close to three times the size of the operation currently being installed.

In a letter to her opposite number Michael Gove, Labour’s Rachel Reeves questioned why, according to reports, outsourcing giant Serco had been asked to provide 18,000 staff “despite some public health professionals suggesting as many as 50,000 staff are needed” on top of the roll-out of the NHS Covid-19 symptoms app.

She said the set-up of the team would have “consequences which are profound both in terms of public health and the economy”.

The debate about schools and safety was prompted by the Government’s decision to announce a phased reopening from the start of next month in England.

There are no plans yet to follow suit in Scotland, Wales and Northern Ireland and teachers’ unions have expressed fears that the move would be too soon due to the risks of infection from coronavirus.

But Education Secretary Gavin Williamson has defended the approach, saying he arranged Friday’s meeting to brief teachers’ representatives on “the scientific advice underpinning our approach”.

Mr Williamson said if the scientists said a “limited number” of children could be sent back to school, it was his duty to allow this to happen.

The Education Secretary assured teachers and parents the June 1 returns would be the first phase of a “controlled and careful” process which would involve a range of protective measures, including keeping class sizes small, making sure children stayed within small groups, observing strict hygiene and cleaning measures, and having breaks and mealtimes staggered to reduce crowding.

Boris Johnson, announcing his plans for taking England out of lockdown, said Reception, Year 1 and Year 6 pupils would go back first.

But National Education Union joint secretary Mary Bousted said a “wider opening of schools, too early, poses a lot of unanswered questions about the risks in poor communities”.

Local authority leaders also accused ministers of going too fast on schools and demanded more local control over their return.

The LGA has said schools should be allowed to make their own decisions about reopening, especially in areas where there is a higher proportion of black, Asian and minority ethnic residents.

Councillor Judith Blake, chairwoman of the LGA’s children and young people board, said parents were “anxious” about sending their children back to school and said more needed to be done to reassure families.

Meanwhile, the UK’s rate of reinfection, known as the R number, appeared to be slowing.

Academics at the University of Cambridge reported that the R rate was now firmly under 1.0 – a goal the Prime Minister has set in order to keep gradually releasing the lockdown in the coming months.

London, according to the university’s MRC Biostatistics Unit, has an R rate of 0.4, the lowest in the country, having once been the worst affected in terms of coronavirus-related hospital admissions.

It means for every 10 people who are infected, they are likely to pass it on to four people, with 24 daily transmissions said to be occurring currently in the capital.

According to the modelling, which is the work of a joint Public Health England (PHE) and University of Cambridge group, the English region with the highest R rate is the North East and Yorkshire, with a transmission rate of 0.8.

Those figures emerged as:

– A study showed that more than a quarter of NHS patients who died in hospitals in England after contracting coronavirus had diabetes.

– Northern Ireland took its first steps towards easing its coronavirus restrictions, with garden centres and household recycling centres to be allowed to reopen on Monday.

– Ministers in Wales prepared to outline their road map for exiting the lockdown later on Friday.

– Transport Secretary Grant Shapps said more than half of people on the Isle of Wight have now downloaded the NHS contact tracing app.

– A mayoral source confirmed to the PA news agency that Transport for London had been granted a Government bailout, after its income slumped by 90% as a result of the lockdown measures.

– Mr Johnson’s fiancee Carrie Symonds joined the Prime Minister on the steps of Downing Street to join in with the national applause for health workers.

The diabetes figures and other research that has found that being obese doubles the risk of needing hospital treatment for coronavirus has prompted Mr Johnson to draw up plans for a “much more interventionist” drive to tackle obesity, according to The Times.

The Prime Minister, who had his own brush with Covid-19, told senior ministers and advisers “I’ve changed my mind on this” and that he was drawing up a new strategy.

Being overweight increases the chances of developing type 2 diabetes.