Devon and Cornwall Police has admitted officers should have dispersed a social gathering in Plymouth on Bank Holiday Monday.
A spokesperson for the force has confirmed two officers attended a planned live-music event at a car park and had engaged with the group.
But they did not send anyone home or enforce government guidance - which stipulates that people must not mingle in groups to minimise the spread of coronavirus.
Police say the event was "not lawful" and "in breach of current legislation" and the officers will receive "advice and training around current powers and its implementation" amid the lockdown.
The meet-up, which saw between 25 and 30 people watch local singers perform in a social club carpark, sparked outcry as witnesses claimed the group were not adhering to social distancing guidelines and were putting local people at risk.
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Organisers claim they went to "great effort" to maintain social-distancing guidelines and say they didn't do anything wrong.
Official government guidelines allow people to sit and rest outside - either relaxing or exercising - alone, with members of their household or "with one other person from outside your household, while keeping two metres apart at all times".
But gatherings in groups are not yet permitted, as previously reported.
Full police statement on 'live music event' in Plymouth
A spokesperson for Devon and Cornwall Police said: "On Bank Holiday Monday, Devon and Cornwall Police were notified of a potential breach of COVID-19 legislation on Pattinson Drive, Plymouth.
"Two officers attended and identified a group of around 20 people in the car park who were holding a socially-distanced charitable event.
"The officers did not take any action and were interacting with [the] group in a light-hearted manner. After this engagement the officers left.
"This event was in breach of current legislation and both officers will receive advice and training around current powers and its implementation in line with the amended regulation which took effect on 13 May 2020.
"Our focus has turned towards groups of three or more people outside of one household, and public gatherings as these are not lawful.
"Officers will always use their discretion to engage, educate and encourage members of the public however, where the evidence is clear and as a last resort, officers will use enforcement options that are available to them."
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Organisers said the event was set-up by a group of friends to help "boost morale" and raise community spirit during this difficult time, especially among the elderly and people who have lost loved ones.
Local singers performed to the group outside, while the social club and community centre building was locked throughout the event, organisers say.
One organiser said the team went to 'great effort' to maintain social-distancing guidelines.
He told PlymouthLive: "Obviously people's safety is paramount, so we all went to great effort to ensure the appropriate measures were in place.
"There were sprayed boxes in the car park. Only members of the same household were permitted in each box.
"There was a one-way system in place to ensure that nobody passed each other whilst walking to and from their box.
"There were also three hand-sanitiser stations.
"Social distancing signage was put up around the car park along with littering signage and a letter for all attendees to read, reminding them of their responsibilities for their own and other peoples safety.
"Bin bags were put in each box to ensure that any rubbish could be bagged up and taken off site.
"The singers also give a talk before they begin stressing the importance of safety."
"I have to say that everybody that turned up were well behaved and respected the rules in place," the organiser added.
What does the law say? According to gov.uk
Guidance - staying alert and safe (social distancing)
Visiting public places
"You can exercise outside as often as you wish and you can also sit and rest outside – exercise or recreation can be alone, with members of your household, or with one other person from outside your household, while keeping two metres apart at all times.
"You may drive to outdoor publicly accessible open spaces irrespective of distance, but should follow social distancing guidance whilst you are there. You should plan ahead to ensure that, where you are visiting places like National Parks, you have checked that they are open and appropriately prepared for visitors. You should not go to ticketed outdoor leisure venues, where there is a higher risk of close contact and touching surfaces.
"When travelling to outdoor spaces, it is important that people respect the rules in Scotland, Wales and Northern Ireland and do not travel to different parts of the UK where their intended activities there would be prohibited by legislation passed by the relevant devolved administration."
