The British spokesman said there had been 100 to 200 people in the crowd.
An 8 p.m. curfew was imposed to keep people off the street, a British military spokesman said.
The British spokesman said that until a change in law earlier this year, homosexual activities in the armed forces were a criminal offense.
A British spokesman said the "war criminals team" was investigating 18 cases, some involving people who had been in Britain for a long time.
British and American spokesmen have worked to discourage reports of divisions between the two principal military allies.
Reuters quoted a British military spokesman as saying that he had been unable to confirm the reports of an attack on the suspected perpetrator.
A British spokesman at the military headquarters in Basra said he would not take questions.
"Talks were very friendly and constructive," a British spokesman said.
A British spokesman said: "Our position has not changed.
So they decided to stay, a British spokesman said.