People struggling to get lateral flow tests “should just refresh” the webpage, the education secretary has suggested.

Secondary school staff and pupils have been asked to test for Covid-19 twice a week when they return to the classroom this week but concern has been raised over the supply after weeks of shortages.

Paul Whiteman, general secretary of school leaders’ union the NAHT, said that recent issues with test supply had made staff “nervous” they will not be available when needed.

Asked on Sky News about a shortage of the tests, Nadhim Zahawi, the education secretary, said the government had tripled the supply to 300 million a month and delivery capacity to 900,000 a day.

He said: “If people feel that they can't get the supply they should just refresh their webpage.”

He also said he had organised a separate supply of tests for schools ahead of children's return to the classrooms.

Mr Zahawi said research from the education commissioner found that being in school was “much better” for the health and wellbeing of children.

“The priority is to keep schools open,” he said. “The testing, the staffing support we're putting in place, and of course the ventilation is going to make a big difference to schools this year.”

He said he thought there was “a big difference from last year to this year”, and promised that all exams this summer would take place.

Along with testing, pupils are also being asked to wear masks in classrooms from this week and an extra 7,000 air cleaning units will be provided to schools to improve ventilation.

Mr Zahawi admitted it was “more challenging, of course, to deliver education with masks on in the classroom”.

But he said: “This is an aerosol-transmitted virus and if you're wearing a mask, if you're asymptomatic, then you're less likely to infect other people.”

He said he hoped the mask guidance would not stay in place “for a day longer than we need it”.

He also told headteachers to consider merging classes or sending groups of children home if the number of staff off work due to coronavirus rises too high.

“We monitor staff absenteeism, I just said to you we're running at about 8 per cent last year. If that rises further then we look at things like merging classes, teaching in bigger numbers.”