British Prime Minister Boris Johnson on Tuesday engulfed in a fresh row over an alleged Downing Street party he reportedly attended with wife Carrie in apparent breach of the country's COVID-19 lockdown rules in May 2020.

The Opposition Labour Party will be raising the issue as an urgent question in the House of Commons as details of a bring-your-own-booze (BYOB) party email invitation sent to around 100 people emerged.

The BBC claims witnesses confirmed that Johnson was present at this so-called Socially Distanced Drinks at 10 Downing Street on May 20, 2020.

"After what has been an incredibly busy period we thought it would be nice to make the most of the lovely weather and have some socially distanced drinks in the No 10 garden this evening," reads the alleged email invite, published by ITV News'.

"Please join us from 6pm and bring your own booze," it adds.

The email invitation was sent reportedly on behalf of Johnson's principal private secretary Martin Reynolds. The rules in place at the time required people to socialise only within their own household or one person from another household in an attempt to contain the spread of COVID-19.

You can meet one person outside of your household in an outdoor, public place provided that you stay two metres apart, was the UK government announcement during a 10 Downing Street coronavirus briefing on the day of the alleged party in May 2020.

The Metropolitan Police said the force was "aware of widespread reporting relating to alleged breaches of the Health Protection Regulations at Downing Street on 20 May 2020 and is in contact with the Cabinet Office", which oversees government policy.

The latest row comes as senior UK civil servant Sue Gray is conducting an investigation into such alleged lockdown breaches within government after previous reports of gatherings. Downing Street has said it would be "inappropriate" to comment as it said this is being looked into as part of the ongoing independent investigation.

The latest gathering first came to light last week in a blog by Johnson's former aide turned nemesis Dominic Cummings. Last month, the Guardian' published a photograph taken on May 15, 2020 five days before the alleged BYOB drinks party showing Johnson, his wife Carrie and 17 staff members in the Downing Street garden.

Johnson had dismissed this as "people at work, talking about work" rather than a gathering.

These allegations have hounded Johnson for some time and in December last year Johnson had appointed Simon Case, the UK's top civil servant, to investigate events taking place in government buildings in 2020 despite coronavirus restrictions being in force. However, the row spiralled further as Case had to step down after suggestions one of the parties had happened in his own office.

PTI