Dominic Cummings, British Prime Minister Boris Johnson's controversial former top aide and architect of Brexit, is set to take aim at the government Wednesday during a marathon grilling from lawmakers.

Cummings, who stepped down as Johnson's chief adviser in December, has launched a series of explosive attacks in recent weeks against his former boss's coronavirus policies and financial dealings.

A divisive figure who carved out a uniquely powerful role during the first 18 months of Johnson's government, he has accused the UK leader of lacking competence and integrity and his government of "appalling ethics".

Boris Johnson and Dominic Cummings
Cummings (R) has launched a series of attacks against his former boss's coronavirus policies and financial dealings Photo: AFP / DANIEL LEAL-OLIVAS

Cummings has previewed his expected testimony ahead of his much-anticipated appearance in front of a parliamentary committee scrutinising the government's pandemic handling, which is scheduled to begin at 9:30 am (0830 GMT).

In dozens of social media posts, he claimed Johnson had adopted a haphazard approach, initially favouring a so-called herd immunity strategy before belatedly abandoning it when the likely death toll became clear.

If Britain had had "the right preparations + competent people in charge", it could probably have avoided its first lockdown in March 2020 and "definitely" escaped later ones, Cummings wrote, as part of a 59-message Twitter thread.

"Given the plan was AWOL/disaster + awful decisions delayed everything, lockdown1 became necessary."

UK vaccination program
Johnson's government has overseen a successful vaccination drive, with more than two-thirds of adults getting at least one dose Photo: AFP / Oli SCARFF

He also accused Health Secretary Matt Hancock of lying about the government's true plans.

Downing Street has denied ever pursuing a herd immunity strategy.

Dominic Cummings
Cummings has also accused Health Secretary Matt Hancock of lying about the government's true plans for the pandemic Photo: AFP / Tolga Akmen

Cummings, the strategist behind the "Leave" campaign in the 2016 Brexit campaign, was appointed chief adviser by Johnson when he took power in July 2019.

He helped to secure a thumping election victory that December, but his frequent clashes with colleagues are said to have led to persistent tensions and he left government a year later.

The 49-year-old was especially blamed for undermining the government's coronavirus lockdown message early in the crisis when he went on a lengthy cross-country journey with his family.

Cummings claimed he and his wife needed childcare help from relatives after they both developed virus symptoms, and that one lockdown-breaching drive to a local landmark was to test his eyesight.

Dominic Cummings
Cummings was blamed for undermining the government's coronavirus lockdown message by going on a trip with his family Photo: AFP / Tolga AKMEN

Critics labelled his defence farcical, and Johnson and his ministers expended considerable political capital backing him at the time.

After Cummings quit Downing Street under a cloud of acrimony later that year, he initially kept a low profile.

However, that changed last month when the ex-aide used his personal blog to claim Johnson had sought to use potentially illegal donations to renovate his publicly funded Downing Street accommodation.

He also made other incendiary claims, including that the Tory leader had raised the prospect of blocking an internal inquiry into leaks because they could implicate a close friend of Johnson's fianc?e Carrie Symonds.

Several investigations have been launched into some of the affairs, including a probe by Britain's Electoral Commission -- which regulates party and election finance -- into the flat makeover.

Johnson had faced growing pressure over the allegations, but bought himself political breathing space after the Conservatives performed well across England in UK-wide local elections on May 6.

However, Cummings' evidence at the parliamentary hearing Wednesday could refocus attention on the government's patchy performance responding to the pandemic.

Britain has been one of the hardest-hit countries in Europe, registering nearly 128,000 deaths within 28 days of a positive Covid-19 test.

In a broader categorisation, nearly 152,000 fatalities in the UK note coronavirus on the death certificate.

But Johnson's government has also overseen a successful vaccination drive, having offered more than two-thirds of adults at least one dose.

The speedy rollout has coincided with a turnaround in its previously falling ratings, and is widely credited with the better-than-expected results on May 6.

Meanwhile, the public may view Cummings' critique with scepticism.

A YouGov poll last week found just 14 percent of respondents trusted him to tell the truth. This compared to 38 percent who trust Johnson.

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