Sir Keir Starmer has urged council leaders to keep schools open as the London mayor called on the government to consider closing them early in the capital ahead of Christmas amid a surge in coronavirus cases.

Sir Keir told his LBC radio phone-in: “I’m very reluctant to close our schools down. I’m worried about closing schools early but, equally, I can see council leaders are put in a difficult situation now.”

Sadiq Khan wants all secondary schools and colleges in London to close a few days early and reopen later in the new year owing to “significant outbreaks” among 10- to 19-year-olds.

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The mayor is also calling for all schools in London to be given priority testing with immediate effect and for extra resources to support online learning.

But Labour leader Sir Keir said he would urge Mr Khan to speak to the government about what can be done to keep schools and colleges open.

It comes as schools in Greenwich have been asked to close and switch to remote learning from Monday evening owing to rising coronavirus rates.

In a letter to parents, Greenwich Council leader Danny Thorpe said the south-east London borough is experiencing a period of “exponential growth” in Covid-19 cases, which requires “immediate action”.

The NEU teaching union is calling on other councils to take the same action as Greenwich.

Asked what he would say to the London mayor, the Labour leader said: “Talk to the health secretary about what we can do this week to keep schools open, try to keep them open this week.”

However, Sir Keir suggested that bringing an extra Inset day forward from the new year would be “smart” in order to close schools a day earlier than planned.

“But the worry about closing schools is all the parents have to decide what they do, that’s very difficult with short notice, and we know from previous experience that for children out of school it’s really difficult for the most vulnerable children,” he added.

Schools in England have been told that they can take an Inset day on Friday so staff can have a “proper break” from identifying potential Covid-19 cases.

But heads have been calling for more flexibility to end in-person teaching earlier to reduce the risk of pupils and staff having to isolate over Christmas.

Schools have been warned they could face legal action if they allow pupils to learn remotely in the run-up to Christmas.

New powers introduced through the Coronavirus Act allow the government to issue “directions” to heads around education provision during the pandemic.

But, should schools fail to comply with directions to remain open, education secretary Gavin Williamson could apply for a High Court injunction forcing them to do so.

Mr Khan said: “With significant outbreaks among 10- to 19-year-olds, the government must consider asking schools and colleges to close early and reopen later in January, with extra resource provided to support online learning.”

In a letter to prime minister Boris Johnson on Sunday, he added: “All schools, sixth form and FE colleges, not just in the boroughs with higher levels of cases but across London, should be given priority testing tomorrow (Monday) and Tuesday.”