A pub chain has apologised after a gay group said staff refused to serve them in a row over their sexuality.
The Labour Party's Lesbian Gay Bisexual and Transgendered Rights group were in the Greencoat Boy pub in Westminster, central London, when a row broke out.
The duty manager is alleged to have refused them service.
Pub owner Punch Taverns said the customers were denied service and it had launched an investigation. The matter was also referred to the police.
James Asser, a member of the group, said: "Everyone involved was shocked and outraged. This attitude is totally unacceptable in this day and age.
"What century are we living in here?"
He continued: "When you encounter prejudice you have to stand up and be counted - at the very least we expect an apology.
"We also want a demonstration that the pub chain takes this very seriously and will make sure it never happens again."
A Punch Taverns spokesman accepted that the customers were denied service and said the pub firm was investigating "on what grounds this took place".
"Punch Taverns seeks to provide welcoming venues to everyone. We are shocked and saddened that a group of our guests did not experience this and would like to apologise," he added.
"We would however like to stress that this is an isolated incident and is not representative of our commitment to diversity.
"We are currently conducting a full investigation of the incident and will report back to the Labour LGBT group with our findings."
The incident became the most viewed trend on social networking site Twitter.
Former Labour deputy prime minister John Prescott Tweeted in support of the group, writing: "Forty years ago we campaigned against a Hull pub that banned 'women and queers'.
"This is disgraceful."