Boris Johnson is considering ‘sealing off London’ if there is a local spike in coronavirus cases, it has been claimed.

The plan could see the M25 being used as a border point in the event of a second wave or if a local lockdown is needed, reports say.

Mr Johnson is said to have discussed new plans on Wednesday during a meeting looking at possible future scenarios as the pandemic progresses. Downing Street described the claims from the Sunday Times as speculative.

However, London Mayor Sadiq Khan said he was unaware of the Government wargame and accused the Prime Minister of ‘totally unacceptable’ behaviour.

It has also been suggested that Mr Johnson considered placing London under stricter restrictions when the country originally went into lockdown.

Mr Khan said: ‘Our surprise is that such far reaching contingency plans have been discussed and tested without the involvement or awareness of London’s government. This is clearly totally unacceptable.’

He wrote to Mr Johnson saying the capital’s authorities ‘cannot do what is right for Londoners if we are excluded from key planning sessions in this way.’

The Prime Minister agreed last week that if infections rose significantly, ‘overnight stays in London would be banned, Londoners could be subject to stay-at-home orders, and close-contact services such as hairdressers would close’, according to the Sunday Times.

The move could be implemented more quickly than the local lockdown on Leicester, amid fears of a quick fire spread of the virus.

But Downing Street sources have distanced themselves from the detail in the reports, calling them ‘speculative’.

Mr Khan’s letter, jointly signed by Peter John, Chair of London Councils, began: ‘It is with great surprise that we read in the Sunday papers that Government held a critical exercise last week in which a major resurgence in Covid-19 infections in London was a central scenario. According to media reports, the plans included using the M25 as a quarantine ring – effectively sealing off the city.’