Britain’s biggest teaching union has seen a surge in membership of more than 50,000 new members since the coronavirus pandemic began, HuffPost UK can reveal.

The huge spike in members for the National Education Union, which means it can now boast nearly half a million teachers among its ranks, emerged as schools in England prepared to go back to full time classroom teaching of pupils next week.

Other trade unions in education and the wider public sector have also seen rises in membership as workers seek greater protection and rights amid the uncertainty caused by the virus crisis.

Unison has seen a net increase of at least 24,000 extra members, and sources within Unite and the GMB said they have seen “tens of thousands” more people join, particularly early in the pandemic.

Other teaching unions have benefitted from the rise in activism. The Association of School and College Leaders (ASCL) has seen a 1,500 jump on top of its 20,000 membership. The NASUWT has also seen an increase, although it could not say by how much.

The TUC and union leaders said that the surge ought to dispel the government’s claims that unions are part of the problem rather than the solution to tackling the pandemic and putting health and safety at the heart of workplaces.

Pressure from teaching unions and heads partly lay behind the U-turn last week from education secretary Gavin Williamson to allow discretionary use of face coverings in communal areas in English schools, with mandatory use in lockdown regions.

The NEU became the biggest union of teachers in Europe after the National Union of Teachers (NUT) and the Association of Teachers and Lecturers (ATL) merged in 2017.

In one week alone at the start of the pandemic it put on 10,000 members, an unprecedented rise.

Internal estimates of the NEU’s rise in membership vary, but insiders said that it soared steadily by 20,000 in May to more than 30,000 in mid summer. Official figures won’t be made public until next year.

A union spokesperson said the increase had been estimated at 32,000, but HuffPost has been told by sources within the union movement that it has now reached 50,000 extra members since March.

In TUC YouTube workshops to spread its best practice with other unions, the NEU has revealed that it has mobilised teachers and support staff online via a string of techniques from Zoom calls to mass town hall phone calls, texts and Facebook and via its new app.

One popular innovation among members has been its ‘checklist’ app that allows staff to see if schools are adhering to the five-point list of benchmarks the union felt had to be met for schools to reopen earlier this summer.

The app, which was downloaded by huge numbers of teachers and its findings swiftly sent to heads by staff reps, is credited by the union for so few schools opening in June.

Boris Johnson had promised that all pupils would have at least four weeks classroom time but was forced to change tack and instead allow only key years back to school before the summer break.

The union has since devised a fresh checklist for the September reopening and has repeatedly called for better contingency planning by government to cope with outbreaks that could force schools to close once more

With Williamson still under pressure to quit over the exams algorithm fiasco, unions aim to hit back at moves to pit teachers against parents and instead turn the focus on what government support is provided.

The NEU, which has a £1 membership offer for newly qualified teachers, has had more than 100,000 members on Zoom calls.

It hosted one Zoom call of 20,000 people, a record for a trade union and the biggest trade union or political meeting of recent years, and has recruited more than 3,000 new workplace reps through mobilising people who used the technology.

Kevin Courtney, joint general secretary of the National Education Union, said: “Our new membership has increased substantially since March.

“The reason is very simple – we have been consistently amplifying the voice of teachers, heads and school staff, who are working hard for every young person in their care but are too often traduced by this government.

“In deeply uncertain times, where far too many loved ones have lost their lives to Covid, unions are playing a crucial role in ensuring all workers are protected. Rarely has it been truer to say that we are stronger together.”

Geoff Barton, general secretary of the Association of School and College Leaders, said: “ASCL membership was increasing before the pandemic began, and has continued to rise over the past six months, with nearly 1,500 new members joining the association.

“During that period we have been sending out bulletins to members on almost a daily basis, as well as running webinars, and providing a great deal of information and support on our website, including a regularly updated set of frequently asked questions.

“We have received very positive feedback from our members, and we know that this has contributed to the rise in membership we have seen. We are very grateful to all those who have put their faith in us and we will continue to do everything possible to support them at this challenging time and beyond.”

Several unions in the public sector have benefitted from worker anger at the government’s handling of the pandemic, although many fear that large scale redundancies in the private sector now loom this autumn once the Treasury’s furlough scheme finally ends.

Even before the virus hit, union membership had risen year on year in the UK. Among the extra 91,000 who joined a union last year, most were women, particularly in health and social care and education.

TUC general secretary Frances O’Grady said: “We are hearing from TUC unions about lots of people wanting to know more and asking to join. The pandemic has caused great anxiety, with worries about safety at work, rights like flexible working and whether their job is safe when the job retention scheme ends. And they see unions as the part of the community that can help them.

“But it is not just about ‘us’ helping ‘them’. It’s a way for workers to come together with their workmates to protect each other’s needs. Yes, unions use central resources to help new members and newly unionised workplaces. But most importantly, we give them training and support so they know how to help each other.

“The pandemic may have also helped to shatter myths about unions from hostile voices. People saw the reality of union reps stepping up in their workplace and neighbourhood to negotiate safety and support in the pandemic.

“And they saw unions stepping up nationally to win support like the job retention scheme. It helps people understand that we’re an open community movement, dedicated to making life better for all of Britain’s working people.”

The Department for Business reported earlier this year that 6.4 million people are now union members, making up 23.5% of the workforce.