Boris Johnson will face sustained pressure from within his own party not to extend the national lockdown next month after senior Tory backbenchers - including Wycombe MP Steve Baker - formed a resistance group.

Former chief whip Mark Harper and ex-Brexit minister Mr Baker will lead a "Covid recovery group" to oppose any extension of the measure in a Commons vote promised by the Prime Minister.

Sources boasted that around 50 Conservative MPs had enlisted with dozens more considering membership.

Mr Johnson argued that the four-week lockdown was needed to prevent an "existential threat" to the NHS and said he expected England to return to a local tiered system when the measures end on December 2.

But he will face continued resistance from the Conservative backbenches if he tries to extend any severe measures, amid growing unrest from his own party over the handling of the coronavirus pandemic.

Mr Harper said: "The cure we're prescribing runs the risk of being worse than the disease.

"The Covid Recovery Group will play its part in helping the Government to deliver an enduring strategy for living with the virus, so that we break the transmission of the disease, command public support, end this devastating cycle of repeated restrictions and start living in a sustainable way until an effective and safe vaccine is successfully rolled out across the population."

The name echoes that of the European Research Group of Tory Brexiteers, which saw Mr Baker help whip Conservatives into opposing then-prime minister Theresa May's Brexit deal.

The group outlined three "guiding principles" calling on ministers to undertake a cost-benefit analysis of restrictions, to end the "monopoly" of advice from Government scientists and to improve measures to tackle Covid-19 such as test and trace.

Sir Graham Brady, the influential chairman of the 1922 committee of Conservative MPs, is among those said to have joined the group. So too are William Wragg and Sir Robert Syms.

The formation of the group came as Government figures on Tuesday showed that 532 more people had died within 28 days of testing positive for Covid-19, the highest figure reported in a single day since May 12 and which brought the UK total to 49,770.

Last week, Mr Johnson suffered a Commons rebellion when 32 Tory MPs defied the whip to vote against the lockdown, which was passed with the backing of Labour and other opposition MPs.

Another 17, including Mrs May, abstained from the vote, with backbenchers expressing alarm at the economic impact of the controls and the curtailment of personal liberties.

There has also been anger over the sums being spent on the mass testing programme to alleviate lockdown measures, with suggestions the Government was prepared to shell out in excess of £40 billion.

Mr Baker said: "This sum of money is absolutely extraordinary - of course we need fast, effective testing but I'm concerned the public will need to see an excellent return on this investment or we risk the Conservatives' reputation for fiscal prudence.

"There are a great many things in this life that are important and necessary but we don't spend unlimited sums on them, even if they are a matter of life and death."

Backbenchers were also incensed that the plans to lock down England again were leaked to newspapers ahead of an official announcement.