MPs have earned at least £6m from second jobs since the start of the pandemic, openDemocracy can reveal.

The highest earners, which include a cabinet minister and a former prime minister, received more than twice their MP’s salary from private companies.

Earlier this week, Tory Owen Paterson resigned as an MP after being found to have broken parliamentary rules. Paterson had lobbied for companies from which he had received more than half a million pounds.

Politicians and campaigners calling for tougher financial rules for MPs said that the findings were proof that outside employment is “corrupting democracy”.

MPs are paid a basic salary of £81,932 but can earn extra for being ministers, or the speaker or chairing committees. However, many earn far more from jobs outside Parliament.

openDemocracy recently revealed that John Hayes has received at least £150,000 over three years from an oil and gas firm. The former energy minister has compared climate activists to ‘Radical Islam’.

One of the highest-earning MPs is former Conservative prime minister Theresa May. Since March 2020, she has made £842,526 giving paid speeches to companies including the American bank JP Morgan Chase and World 50 Inc, an exclusive club for senior executives.

Health secretary Sajid Javid also found lucrative second jobs after he resigned as chancellor in February 2020, becoming an adviser to American bank JP Morgan Chase in August last year and AI software company C3.ai just months later.

Javid stepped down from both roles, which would have paid him a combined annual salary of more than £300,000, when he rejoined the cabinet in June.

“Being an MP is not only a privilege but it is also a well-paid and full-time job. It’s totally wrong that some MPs are lining their pockets by moonlighting in other roles and it is sickening that this was being done during a public health crisis,” said Labour MP Richard Burgon.

“These so-called advisory and consultancy roles that some MPs get gifted are corrupting our democracy,” he added. “In the coming days, I will be bringing a bill to Parliament to put an end to this racket by banning MPs from having second jobs, except in some very limited circumstances.”

There has been renewed concern over MPs’ outside earnings amid a scandal over paid lobbying.

On Wednesday, the government voted to prevent Paterson from being suspended for breaching lobbying rules and to instead set up a new committee to review how MPs are investigated for misconduct.

Paterson subsequently resigned on Thursday after the government said it would allow a vote on his suspension following a widespread backlash, including on the Conservative back benches.

Steve Goodrich, head of research and investigations at Transparency International UK said that “recent events show there is far too much room for confusion and mischief”.

“Although the rules provide a ban on most types of paid advocacy by parliamentarians, when MPs take second jobs there’s always a risk that the interests of their employer do not align with those of their constituents,” he said.

Several MPs have also increased their income since the start of the pandemic. In July, senior Tory MP John Redwood was awarded a bonus of £35,000 from wealth management firm Charles Stanley & Co, on top of the £312,120 he has received from the firm during the pandemic.

While Bill Wiggin, the Tory MP for North Herefordshire, received £25,000 in bonuses and director’s fees alone this year, on top of his £49,140 salary as a director of a wealth management firm in the tax haven of Bermuda.

MPs earned £4.9m from second jobs from March 2020, when the first lockdown began, to the following year. They have received at least £1.9m more in the months since, according to figures in the members register of financial interest.

Susan Hawley, head of Spotlight on Corruption, said the government should hold a review into MPs’ second jobs.

“It should look at whether there needs to be far greater scrutiny and transparency about what kind of jobs MPs take, how conflicts of interest are being managed, whether there should be earning caps on how much MPs can earn, and how second jobs impact on MPs ability to fulfil their role as a public servant,” she said.

Writing for openDemocracy this week, former shadow Cabinet Office minister Jon Trickett called for a ban on MPs holding second jobs.

“It should be a full-time job to effectively represent 75,000 constituents and one that does not allow time to represent other paid interests,” he wrote. “MPs are well paid and receive generous expenses. There is no place for additional employment or payment.”