Sending all children back to school - and freeing parents to go back to work - could trigger a second wave of coronavirus, warn researchers.

UCL and the London School of Hygiene and Tropical Medicine team said testing and tracing contacts of those with the virus might help prevent this. But the current test and trace system would need to be more effective.

The study is the first to assess the extent of contact tracing that will be needed to prevent a second wave.

It used computer models to see how the virus might spread as pupils returned to the classroom and their parents were freed from childcare and able return to work or other activities.

The academics investigated the impact of the "phased return" strategy in England. They analysed what happens when Reception, Year 1 and Year Six go back at the start of June; followed by all primary school pupils in July; secondary pupils in Year 10 and 12 having some contact in July and all secondary schools going back in September.

The study showed the combined effect on pupils and parents would be enough to cause a second wave without an effective test and trace programme.

This would happen around December 2020 and would be twice as big as the first peak, unless the government took other actions such as re-imposing lockdown.