Scotland Yard officers were today investigating claims by a gay group that they were not served by a pub in a row over their sexuality.
The Greencoat Boy pub in Westminster, central London, is at the centre of a storm of outrage after news of a confrontation was posted online.
Members of the Labour Party's Lesbian Gay Bisexual and Transgendered Rights group said around 50 members were denied drinks.
Punch Taverns, which runs the pub, has suspended a manager and apologised while an internal investigation takes place.
Police were called to the pub in Greencoat Place, a short distance from Parliament, on Saturday night after members turned up after their annual general meeting.
James Asser, of the group, claimed the manager said he would not have accepted the booking if he knew the group were gay.
He said: "The fact that our members were on the receiving end of homophobia is just wrong. We were surprised by the shocking action of the Greencoat Boy public house management.
"Turning people away for being gay is outrageous - he should have been defending his customers from homophobia."
The campaigning group used the online message service Twitter to alert others and the row became one of the website's most popular topics.
It led to messages of support from senior party figures including John Prescott and Ed Balls as well as Sarah Brown.
Mr Prescott wrote: "40 years ago we campaigned against a Hull pub that banned 'women and queers.' This is disgraceful."
Later he added: "Looks like the deputy general manager of the Greencoat Boy might have had his last orders."
Meanwhile more than 1,500 people signed up to a Facebook campaign calling for a boycott of the pub.
A Punch Taverns spokesman said staff are co-operating with police and have contacted all pubs in the chain to remind them of equality.
He said: "We are shocked and saddened that the Labour LGBT did not experience this at the Greencoat Boy and apologise unreservedly.
"We would like to stress that this is an isolated incident, we have a good track record on equal opportunities and we do not tolerate homophobia in our pubs, whether from guests to other guests, or involving our employees.
"We are currently conducting a full investigation of the incident and the deputy general manager will not be on site until the investigation is concluded."
A Met Police spokesman said: "We can confirm an allegation that a homophobic incident took place and was reported to police. Inquiries by officers continue."