The chief executive officer of British Airways had to be taken away under police escort after demonstrators stormed the building where he was in negotiations with cabin crew about planned labour stoppages, Scotland Yard said.
Willie Walsh needed the police escort on Saturday to get out of the building after the demonstrators managed to get up 23 floors to the level where the talks were taking place.
British Airways' cabin crew has threatened to start a 15-day strike on Monday evening in a dispute over work schedules, pay and conditions.
Press reports described the talks breaking down in chaos after members of the Socialist Workers Party invaded the building, many of them jeering at Walsh as he was escorted out of the building.
More than 50 demonstrators were removed from the building.
British Airways criticised Derek Simpson, co-leader of the trade union Unite, with which the talks are being conducted, for posting comments about the ongoing negotiations on the social networking site Twitter, perhaps inciting the protest.
Unite officials said they had nothing to do with the interruption. Tony Woodley, the other co-leader of Unite, was seen angrily shouting "shut up" at the interrupting protesters. The Press Association cited sources saying some progress had been made during the meeting before the interruption.
In a statement, Unite said the protests and the references to Twitter posts were irrelevant to the negotiations.
"We stand ready to resume talks with BA at any time. We urge that the distractions of today are set aside and that no time is wasted in getting back to the vital business of making progress and settling this dispute."