New restrictions banning different households from mixing indoors could be imposed on London as early as this week to prevent rising coronavirus levels, mayor Sadiq Khan has warned.

The city is expected to be initially placed on ‘medium’ in the new three-tier system of local alerts for England when they come into force on Wednesday.

This would put London with most of the nation at the lowest end of the scale, meaning no new restrictions would be imposed immediately and the rule of six and the 10pm curfew staying in place.

But the London Mayor warned that the capital could be moved upwards ‘very quickly – potentially even this week’ after Prime Minister Boris Johnson set out his plans on Monday.

If the city moves up a notch to ‘high’, then mixing between different households or social bubbles could be banned indoors, including in pubs and restaurants.

A spokesman for Mr Khan said: “The virus is now spreading very quickly in every corner of London. The number of cases is rapidly increasing and all the indicators we look at are moving in the wrong direction.

“As of today, London is at ‘medium’ in the Government’s new alert levels. However, Londoners should understand that this could change very quickly – potentially even this week.”

The mayor discussed the new alert system with local leaders in the capital on Monday, and they are understood to have agreed further restrictions will soon be needed if the figures continue on the current trajectory.

His spokesman added: “Discussions with London leaders, scientific advisers and the Government will continue over the coming days and the mayor will be as clear as possible with Londoners about what they can expect as soon as possible.

“Nobody wants to see new measures that will impact on businesses in London such as the hospitality sector – least of all the mayor – but we have a responsibility to act on the evidence if it will save lives.”

Groups of up to six people would still be able to meet outdoors in public spaces and private gardens if the capital was moved into the “high” level.

Mr Johnson told MPs that “most areas” currently subject to heightened restrictions would be placed at this level, but so would Nottinghamshire and East and West Cheshire.

Nottingham has the highest Covid-19 rate in England, with 843 new cases per 100,000 in the seven days up to October 9. Cheshire West and Chester is on 167 and Cheshire East is on 146.

The London-wide average was 78 new cases per 100,000 over that week, far lower than those areas, but the level varies widely across the capital.

Ealing in the city’s west was faring worst with 119 new cases while Bexley had the lowest number of new cases at 51.6.

But despite the range of rates across the capital, the current intention is understood to be for any new restrictions to be imposed across the capital as one.