Updated 6.24pm

British Prime Minister Boris Johnson's top aide Dominic Cummings defied calls to resign on Monday over allegations that he broke coronavirus rules and undermined the government's response to the health crisis.

The Brexit campaign mastermind told reporters he had acted "reasonably and legally" when he drove across the country with his wife while she was suffering from the virus in early April.

Britain was then recording hundreds of deaths daily and following strict lockdown rules requiring people with even the slightest symptoms to stay at home for at least a week.

"I have not offered to resign. No, I did not consider it," a visibly nervous Cummings said in his first press conference on the job.

"In this very complex situation, I tried to exercise my judgement the best I could. I believe that in all circumstances I behaved reasonably and legally."

Cummings did not apologise for his behaviour but did express regret for not asking Johnson -- himself already hospitalised for COVID-19 -- for permission to travel during the lockdown's most restrictive phase.

"Arguably, this was a mistake and I understand that some will say that I should have spoken to the prime minister before deciding what to do," Cummings said.

Cummings became British Prime Minister Boris Johnson's trusted lieutenant after helping him score stunning ballot box successes.

But his tactics and abrasive personality made enemies across the political spectrum.

Johnson is now facing sustained pressure to fire his right-hand man for flouting coronavirus lockdown rules that Cummings himself helped to draft.

 

Cummings was the mastermind behind the campaign that saw Britain vote to leave the European Union in 2016.

He was portrayed by actor Benedict Cumberbatch in a TV dramatisation of the seismic referendum which divided the nation and led to years of crippling political infighting.

His aggressive campaigning tactics, including an infamous Brexit campaign bus emblazoned with a questionable promise of funding for the country's National Health Service, turned him into a lightning rod among many opposed to Brexit.

Former prime minister David Cameron called him a "career psychopath" because of his confrontational style, which also made him unpopular with many Conservative MPs and staunch Brexiteers, who were among those calling for his head. 

'Hypocritical elitism' 

Cummings' electoral successes were partly built on tapping into widespread frustrations with the political classes, and his own disdain for the "Westminster Bubble" and mainstream media.

But for a man claiming to be more in touch with the public, he misjudged the mood badly by claiming it was "the right thing to do" by travelling some 250 miles (400 kilometres) to be near his family in Durham, northeast England.

That angered many people who abided by the lockdown rules, in some cases missing a chance to say a final goodbye to loved ones who died from the virus, or attend their funerals.

Guardian journalist Jonathan Freedland tweeted that Cummings had become the "face of... a hypocritical Westminster elitism" that he himself had railed against.

Johnson hired Cummings after becoming leader in July, when the government was bogged down in its attempts to leave the European Union and parliament was unable to agree on a divorce deal. 

He hoped Cummings' reputation for unconventional and bold action would help him break the deadlock.

The move paid off, and after calling a snap election in December, he secured an 80-seat majority, setting the seal on Britain's departure from the European Union in January.

'Weirdos and misfits' 

Johnson also trusted Cummings with his ambitious big-spending plans to modernise the British economy and state, giving him unprecedented powers as an aide.

The 48-year-old famously sent out a call for "weirdos and misfits" to join his policy unit, which would be driven by science geeks and "artists" to break up what he saw as the civil service's stranglehold.

His dress sense -- more Silicon Valley than Westminster -- earned him the title of the world's worst-dressed man from GQ Magazine.

"Nondescript sports hoodie and jeans... why does Boris Johnson's political disruptor dress like an unlicensed cab driver?" it asked.

Oxford University-educated Cummings, the son of an oil-rig worker and a teacher, first worked in government as an adviser to then-education minister Michael Gove, following a stint working in Russia as it emerged from Soviet ruins in the 1990s.

He soon became a thorn in the side of the civil service, which he called the "blob" for resisting his reform plans that were described by Guardian journalist Patrick Wintour at the time as "either mad, bad or brilliant".

But it was during the 2016 referendum campaign that he made his name, although he was contemptuous of many of those campaigning alongside him.

He later called leading Tory Brexit supporter David Davis "thick as mince" and "lazy as a toad" while anti-EU figurehead Nigel Farage said he "had huge personal enmity with the true believers in Brexit".

Two of those "true believers", Steve Baker and Peter Bone, were among the first Tory MPs to break ranks and demand his sacking.

Baker called Cummings a "dominant figure who regards accountability with contempt". 

Writing in The Critic magazine, he described Cummings as "one who venerates science beyond reason and whose response to every serious problem is, metaphorically, to drag someone into the public square and chop off their head."

But Johnson said Sunday that Cummings "acted responsibly and legally and with integrity".