Schools are struggling to cope with a lack of Covid-19 tests for pupils and staff as the situation is becoming “increasingly out of control”, a teaching union leader has warned.

Dr Patrick Roach, general secretary of the NASUWT teaching union, has called on the Government to prioritise the education sector for the allocation of tests in light of widespread challenges.

Three organisations representing school leaders and governors have also implored Boris Johnson to “take charge” of tackling the delays in obtaining Covid-19 tests to ensure schools remain open.

The letter – from the Association of School and College Leaders (ASCL), school leaders’ union NAHT and the National Governance Association (NGA) – warns heads are in an “impossible situation”.

The ASCL said it has received 264 responses from schools and colleges in recent days where leaders have said they have symptomatic staff and/or pupils who were struggling to access tests.

“Schools are left in a position of either leaving close contacts of the infected person in school while they wait for guidance, or making a public health call themselves and deciding on who to send home,” the letter says.

But addressing concerns about testing when appearing before the Commons Education Committee on Wednesday, Education Secretary Gavin Williamson said each school was given 10 home-testing kits at the start of term and schools can now order more kits from the NHS directly.

Rob Halfon, chairman of the committee, asked if he could “guarantee” that pupils and teachers who need local Covid-19 tests would be able to get them within 48 hours in the event of outbreaks.

But Mr Williamson replied: “Schools are, I think, the only organisation that actually has a set of testing kits that have been sent to them directly in order to be able to ensure that if they are in a situation where someone isn’t in a position to be able to get a test, then they actually have testing kits on site.”

Schools have been hit with Covid-19 cases since it became compulsory for pupils to return.

Some have closed their doors days after reopening while others have told whole year groups and classes to self-isolate for two weeks following confirmed cases.

In a letter to schools minister Nick Gibb, Dr Roach said: “Schools appear to be seeking to do their utmost to carry on.

“However, we have reports that schools are unable to cope with a situation that is becoming increasingly out of control.”

Local authorities across the country – including in the North West of England – are struggling to cope with the demand for tests from schools, he added.

Dr Roach said: “In particular, areas where additional local restrictions have been introduced due to the increase in the R-number are now unable to cope with demand for tests.

“Teachers, support staff and children and young people are unable to access tests where they have Covid-19 symptoms.

“Employers are struggling to deal with the implications and consequences.”

The letter says members have reported that hundreds of pupils in Bury are self-isolating, while Salford council has been inundated with requests for tests from schools.

The Mayor of Greater Manchester said around 110 schools in the area had reported coronavirus cases.

A poll from the GMB union suggests only half (51%) of school staff have had training on Covid-19 health and safety measures and working practices – including infection control and correct use of PPE.

Stuart Fegan, national officer of GMB, said it is “shocking” that large numbers of school staff are missing basic health and safety training around Covid-19 since schools had fully reopened.