The Metropolitan Police have rejected a request from lawyers to pursue protesters who disrupted a Proms concert by the Israeli Philharmonic Orchestra at London's Royal Albert Hall last September.
UK Lawyers for Israel had argued that charges of aggravated trespass could have been brought against some of those who took part in the protest.
But Jonathan Turner, chairman of the lawyers group, said the police had responded that they did not intend to act because the management of the hall would not assist them.
Mr Turner commented: "We consider this regrettable since we think that criminal offences were clearly committed and that the police could have secured convictions even without the co-operation of the Royal Albert Hall."
He added: "The failure to deal with the problem now will store up more trouble in the future. Many eye-witnesses have described the threatening atmosphere which resulted from the repeated interruptions and we fear that there could be a serious breakdown of public order on another occasion."
It was "particularly unfortunate," he said, "that the Royal Albert Hall management declined to co-operate. We hope and expect other organisations to be conscious of their civic responsibilities."
A police spokesman said that officers from Westminster had considered complaints received after the incident and "concluded no offences had taken place. The matter is therefore now closed."
The Royal Albert Hall declined further comment beyond its statement after the event, when it said that "however much we regret that the disturbances took place within the hall, rather than outside, we have no intention of pursuing any further course of action."
Mr Turner said the possibility of a private prosecution had been considered but the group "decided in the end not to pursue it".