Gospel singer Harmonie London, 20, regularly performs worship music to passing shoppers on Oxford Street and has more than 300,000 subscribers on YouTube.
But she was stopped by a Metropolitan Police special constable and told: 'No miss, you're not allowed to sing church songs outside of church grounds, by the way.'
It is not entirely clear whether the officer was accusing Harmonie of breaking the law in the area, which is a council-regulated zone for busking and street entertainment.
There are no laws against singing on pavements - and Harmonie said the incident breached Article 9 of the Human Rights Act which protects freedom of religion.
As onlookers watched and filmed outside the John Lewis store, Harmonie protested her innocence to the officer, saying: 'You are, you are (able to sing church songs).'
But the officer continued to insist that Harmonie could not sing 'outside of church grounds unless you have been authorised by the church to do these kind of songs'.
Harmonie said 'that's a load of rubbish, you're allowed' - but the officer then walked away and another said: 'She's not saying anything anymore, thank you for your time.'
The singer said: 'Are you saying that you don't care about the Human Rights Act?'
She then accused the officer of 'laughing' while she was walking away. The officer then stuck her tongue out.
In a later video, Harmonie quoted Article 9 of the Human Rights Act 1998 which protects someone's right to freedom of thought, belief and religion.
Among those hitting out at the video was former Conservative minister Ann Widdecombe, who called for the officer to be 'struck off from the voluntary force'.
She told GB News: 'She really has got the law completely wrong and she was obviously enjoying herself rather too much, trying to boss this woman around.
'And there is no basis at all for saying you can't sing. I could walk down the street singing Onward Christian Soldiers and I would be committing no offence at all.'
Norman Brennan, a former police officer and anti-crime campaigner, also tweeted: 'Folks, this is not a good look. Some of us are trying hard to help policing get back public lost support respect and confidence and this does not help.'
And Andrea Williams, chief executive of the Christian Concern campaign group, told MailOnline: 'One of my favourite things as I commute to work is to hear Harmonie's beautiful worship.
'She blesses tens of thousands of people in the same way and brings harmony to the streets. We need more of this, not less. It is shocking that she has been treated like this.'
Former Metropolitan Police detective Peter Bleksley also commented on the video, tweeting: 'Lawless Britain. The woman in uniform that is…'
And former Home Office special adviser Claire Pearsall told TalkTV: 'Really should the police be going around telling people they can't sing, they can't pray, they can't think something? Why don't they go and deal with actual crime?'
Harmonie London has become a popular Christian street singer in recent years and now has nearly 300,000 followers on each of Instagram and YouTube.
Some of her videos have attracted more than four million views. Her latest clip posted yesterday was entitled: 'Unpaid Volunteer Officer Doesn't Like Gospel Songs.'
The caption for the clip, posted at about 6pm, said: 'Special constables are volunteer police officers who invest their free time to make a real difference to our city. You will get a tremendous amount of pride from giving back to the community.'
Scotland Yard confirmed to MailOnline that the video was filmed on Oxford Street at the weekend, with officers now 'working to understand the context in which these comments were made'. The force said an update will be issued 'as soon as we can'.
Harmonie's clip of the confrontation has so far attracted more than 5,000 likes and 1,500 comments. MailOnline has contacted the singer for comment.
Westminster City Council includes the Oxford Street area among its busking and street entertainment regulated zones of the West End.
Policy states that there is a 'light touch licensing scheme' applicable in the area, which means anyone will 'only be able to busk in designated pitches'.
They also need to apply for a licence to perform, keep to terms and conditions of the designated pitches, and abide by the conditions of their licence.
Busking is not illegal in England and Wales but there may be certain byelaws or rules imposed by individual councils, such as not making too much noise.
Singers also may to told to avoid blocking pavements, not displaying notices asking for payment and only busking in certain parts of a town or for a fixed period of time.
Special constables are volunteer officers who have the same powers as a regular officers and work at least 200 hours annually, equating to 16 hours per month.
Specials are based on one of the 12 basic command units across the 32 London boroughs and also wear the same uniform as regular officers.
Their duties include responding to 999 calls, foot and vehicle patrols, tackling antisocial behaviour, road safety initiatives and house-to-house enquiries.
They also present evidence in court, help police events and take part in 'hotspot' operations to tackle underage drinking, criminal damage and public disorder.
Those involved – who normally have a full or part-time job as well - can benefit from free travel within London and a discount on council tax within Greater London.
Other officers have been criticised for heavy-handed policing of buskers in recent years - including one in 2021 left covered in blood as he was held to the ground by five officers following an apparent row over performing in public in Bournemouth.
Also in 2011, a York busker was fined £200 for allegedly breaking Covid restrictions by playing the piano because police said it was causing people to congregate.
And in Northampton last month, it was revealed that buskers considered a 'nuisance' in the town centre would be told to stop playing under new council rules.