Professor Neil Ferguson will not face further action by police after accepting he made an "error of judgment" by breaching social distancing rules despite being a key figure in influencing the lockdown.
Scotland Yard criticised his behaviour as "plainly disappointing" but ruled out issuing a fine because he "has taken responsibility" after resigning as a key Government adviser in the coronavirus response.
The researcher, whose work was crucial in Boris Johnson's move to enforce strict conditions, stood down from the Scientific Advisory Group for Emergencies (Sage) after allowing a woman to visit him at his London home.
Health Secretary Matt Hancock said the Imperial College London professor had made the "right decision to resign" but that it was a matter for police to decide whether to take further action.
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He told Sky News that it was "just not possible" for Prof Ferguson to continue advising the government.
Mr Hancock said the social distancing rules "are there for everyone" and are "deadly serious".
Scotland Yard said: "We remain committed to our role in supporting adherence to Government guidance and have made it clear that our starting position is explaining the need to follow the regulations with anyone who is in breach in order to keep people safe and protect the NHS.
"It is clear in this case that whilst this behaviour is plainly disappointing, Professor Ferguson has accepted that he made an error of judgment and has taken responsibility for that.
"We therefore do not intend to take any further action."
Prof Ferguson's modelling of the virus's transmission suggested 250,000 people could die without drastic action.
In a statement, Prof Ferguson said: "I accept I made an error of judgement and took the wrong course of action.
"I have therefore stepped back from my involvement in Sage (Scientific Advisory Group for Emergencies).
"I acted in the belief that I was immune, having tested positive for coronavirus and completely isolated myself for almost two weeks after developing symptoms.
"I deeply regret any undermining of the clear messages around the continued need for social distancing."
He also called the government advice on social distancing "unequivocal", adding that it was there "to protect all of us".
The Telegraph reported that Antonia Staats visited his home on at least two occasions during the lockdown.
Prof Ferguson, a mathematician and epidemiologist, led the Imperial team that modelled the spread and impact of Covid-19 in a Government-commissioned report.
The paper said merely slowing the spread of the virus, which had at that point been the aim, would have led to the NHS being overwhelmed by cases.
Around 250,000 people could have died in the UK in that scenario but the research said stricter measures would drastically reduce this.
The Prime Minister then announced the lockdown on March 23, ordering the public to stay at home as he shut most shops and gave police unprecedented enforcement powers.
Under those measures, partners who do not live together were told they could no longer see each other.
Mr Johnson today told the House of Commons that measures could be eased from this Monday "if possible".
Imperial College London said Prof Ferguson "continues to focus on his important research".
