In an embarrassing security breach, two environmental activists impersonating hotel serving staff managed to outsmart Stephen Harper's protective detail and stage a protest within arm's length of the Prime Minister as he talked pipelines and trade in Vancouver.

The stunt not only exposed flaws in the Prime Minister's security, but also overshadowed the pro-business message Mr. Harper was trying to deliver in the heart of the province most opposed to the Northern Gateway pipeline project that would ship Alberta oil sands crude to the B.C. coast.

The RCMP, who guard the Prime Minister, vowed quick action on the breach. Spokeswoman Corporal Lucy Shorey said the Mounties are reviewing the incident and "appropriate action will be taken accordingly" afterwards. "The RCMP takes this matter very seriously."

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The activists, later identified as Sean Devlin and Shireen Soofi, appeared behind Mr. Harper just as he was beginning a 30-minute question-and-answer session with Vancouver Board of Trade president Iain Black on Monday.

They brandished signs accusing Canada of a lack of action on climate change before Mounties appeared to guide them offstage. Groans of disapproval could be heard from the business audience on hand for the event at the Fairmont Pacific Rim Hotel.

The Prime Minister, who was seated as this happened, made light of the matter as the protesters were escorted out. "It wouldn't be B.C. without it," Mr. Harper said.

It was unclear how the two protesters managed to get so close to the Prime Minister despite a security screening for the event that included using a bomb-sniffing dog to check journalists' bags and cameras.

Randy Fincham, spokesman for the Vancouver Police Department, said both protesters were detained following their demonstration but have since been released. "Charges have yet to be determined," Mr. Fincham said.

It cost the protesters very little to foil RCMP security, Mr. Devlin recalled in an interview. The pair dressed in garb that made them appear to be part of the hotel staff at the Board of Trade event.

"It was really simple," he said. "We were both just wearing black pants and black dress shirts and we had black aprons on that we bought at Value Village for $7."

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Mr. Devlin said he was held face down on the floor of the hotel's kitchen for a time and then handcuffed and escorted to a police paddy wagon.

Jason MacDonald, director of communications for the Prime Minister's Office, refused to discuss the matter. The PMO never comments on the RCMP security that surrounds the Prime Minister when he's in public.

But Mr. Harper has previously signalled that he was impressed with his protective arrangements. He appointed Bruno Saccomani, the former head of the Prime Minister Protection Detail, as Canada's ambassador to Jordan. Mr. Saccomani earned a reputation as a demanding RCMP boss who drove an effort to beef up prime ministerial protection.

Security expert Michel Juneau-Katsuya, a former senior intelligence officer with the Canadian Security Intelligence Service, said the Vancouver incident, while just a stunt, nevertheless made the RCMP look foolish. "It's very embarrassing, unavoidably embarrassing. They're just lucky in their bad luck" that it was merely a protest, he said.

Mr. Juneau-Katsuya said the Mounties – as proficient at leaders' security as the U.S. Secret Service, in his estimation – will definitely change security rules as a result. He predicted the security of venues that play host to Mr. Harper in the future will also be stepped up.

The Mounties have been embarrassed in the past, most notably in 1995 when an intruder broke into 24 Sussex while prime minister Jean Chrétien and his wife lived there. Also, in 1996, Mr. Chrétien tangled with a protester on Parliament Hill in what became known as the "Shawinigan Handshake" incident.

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Iain Black, the Vancouver Board of Trade president who was hosting the prime minister, said in an interview after the event that he felt "totally safe" when the protesters took to the stage because the activists seemed more intent on making a political point than causing harm.

"I took my lead from the prime minister. He didn't seem ruffled," said Mr. Black.

The former BC labour minister, who left politics in 2011 to become president of the board of trade, said he saw one of the protesters approach and drew some calming conclusions.

"They didn't look like they were there to harm anybody," he said. "In the half second it took me to process what was going on, I didn't feel fear."