POLICE do not plan to undertake a formal investigation into the party at No 10 that broke lockdown rules in May 2020 unless an internal probe finds evidence of potential criminal offences.

Senior civil servant Sue Gray is examining a series of parties and gatherings held in No 10 and Whitehall in 2020 while coronavirus restrictions were in force.

The Metropolitan Police said it will only consider whether to launch its own investigation if Gray's internal probe, "identifies evidence of behaviour that is potentially a criminal offence".

That's despite Boris Johnson apologising for attending a “bring your own booze” party in the Downing Street garden during the first coronavirus lockdown, but insisted he believed it was a work event and could “technically” have been within the rules.

The prospect of a police investigation had led to the possibility that the inquiry could be paused, but a Scotland Yard statement said: “The Met has ongoing contact with the Cabinet Office in relation to this inquiry.

“If the inquiry identifies evidence of behaviour that is potentially a criminal offence it will be passed to the Met for further consideration.”

WATCH: Sky News host comes up with ridiculous excuse for parties at No 10

An leaked email, sent by the PM's principal private secretary Martin Reynolds, urged 100 staff to "make the most of the lovely weather" by attending "socially distanced drinks" in the No 10 garden.

The move comes as lawyers warned a failure to investigate the party be unlawful.

Good Law Project wrote on Twitter: “The Met seem to be operating a two-tier system, with one rule for those in power and one rule for everyone else. Enough. We're suing.”

Elsewhere, they added: “In what other crime would police decline to investigate because the suspect assured them no rules had been broken?

“It is not good enough for the Met to delegate their investigative duties to the press and civil servants. We don’t believe they would make such concessions for anyone else accused of breaking the law.”

READ MORE: Met Police sued over refusal to investigate lockdown-busting parties at No 10

The non-profit said they had instructed Bindmans LLP, and Danny Friedman QC and Adam Wagner are acting as counsel.