As protesters caused headaches for the police in Docklands, a row was brewing today over the powers used by Met officers in stopping suspects.

Demonstrators opposing the 2003 London arms fair and conference (DSEi) claim, and police have admitted, that powers from the 2000 Terrorism Act have been used to search and question individuals.

The Home Secretary this afternoon became involved in the dispute, asking senior officers to explain why the powers, given in section 44 of the Act, were being used at a demonstration, rather than more applicable public order legislation.

DAC Andy Trotter, in charge of policing the event, said this afternoon: "Section 44 is a powerful piece of legislation and we genuinely do not want to misuse it.

"Our officers are being briefed to ensure they are all aware of this. However London is on a high state of alert given the 911 anniversary, the scale of this exhibition and the fact that The Docklands has been subject to acts of terrorism before, and of course we are having to consider the terrorism threat here."

At least four protesters, including three women, were arrested this afternoon during violent scuffles with police.

The scuffles broke out as police attempted to contain a group of around 100 demonstrators blocking carriageways in both directions along the Victoria Dock Road.

One protester said: "They just lost patience in the end. They were arresting people who had done nothing, just to try and break up the protest."

Almost as soon as police had cleared the first protest, a second, smaller wave followed, as protesters fled police, blocking the road again.

Though fairly short-lived, the roadblocks were formed soon after another activist strapped himself to the roof of a train, temporarily halting the Docklands Light Railway between Canning Town and Beckton.

With so many routes of access to the conference centre blocked, arms traders who had already found themselves forced to use buses - alongside the protesters opposing their conference - now began to appear walking along the road alongside the same demonstrators.

As they entered the ExCel exhibition centre, delegates were challenged by protesters. One man shouted: "How many people do you have to kill to line your pockets? What do you spend your blood money on?"

Protests are expected to continue into the evening, and for the rest of the week.