The British capital will move into the toughest top tier of the three-level Covid-19 alert system from early Wednesday after health secretary Matt Hancock told the House of Commons on Monday that there has been a “very sharp exponential” rise of cases in recent days.

Hancock also revealed that a new variant of Covid-19 had been detected, which may have caused the spike in cases in London, Essex and Kent. The World Health Organization, he said, had been informed of the variant, which is unlikely to cause more serious disease than others.

He said: “We have identified a new variant of coronavirus, which may be associated with the fastest spread in the south-east of England. Initial analysis suggests that this variant is growing faster than the existing variants”.

“We’ve currently identified over 1,000 cases with this variant, predominantly in the south of England, although cases have been identified in nearly 60 different local authority areas, and numbers are increasing rapidly”.

A city under Tier 3 is subject to the tightest restrictions, including the closure of pubs, cafes and restaurants; inability to mix indoors, in private gardens or in most outdoor venues, except within a household or bubble.

Indoor entertainment venues – such as bowling alleys and cinemas – must also stay closed, and people are advised not to travel to and from Tier 3 areas. The review of the alert system was due on Wednesday, but was advanced due to the spike in new cases.

Hancock called or continued vigilance in what he called “the final stretch”, since “it is not over yet…there is not a moment to spare”, but noted that the mass vaccination programme has begun, besides increased testing.

Besides Greater London, the new areas under Tier 3 are parts of Essex and Hertfordshire.

London mayor Sadiq Khan said: “The surge in coronavirus cases across our capital is deeply concerning…If the Government does decide to introduce further restrictions in London this week, the economic impact on businesses could be catastrophic with hundreds of thousands of livelihoods at stake”.

“2020 has been a dismal year for our once-thriving hospitality sector and world-famous cultural scene, which both contribute billions to our economy and attract millions of visitors. Without protecting them, there can be no meaningful recovery”, he added.