Civil rights campaigners have condemned the use of anti-terrorism measures against protesters at Europe's biggest arms fair in London.
Police expect a 'challenging day' on Wednesday as protests continue
Civil rights group Liberty said it hoped to go to the High Court to challenge what it saw as a police decision to ban protesters using the "emergency powers".
A total of 79 people have been arrested in connection with the show - which began on Tuesday - since 1 September, Scotland Yard confirmed.
On Wednesday two protesters managed to halt the main public transport route used by delegates to get to the site at the ExCel Centre after chaining themselves to two trains.
Some police officers had used sections 44 (1) and 44 (2) of the Terrorism Act 2000 to stop and search protesters "where they deemed it necessary," Scotland Yard told BBC News Online.
But a spokesman said nobody had actually been arrested under the act, with Metropolitan Police officers holding people for offences ranging from highway obstruction, to assault and possession of cannabis.
Liberty spokesman Barry Hugill condemned the use of anti-terrorism measures against protesters.
One protester was arrested after locking himself to a train
He said: "We have clients who have had anti-terrorism orders served on them. To use it as they are using it against protesters at an arms fair seems to us to be blatantly illegal.
"The notion of using anti-terrorism legislation cannot be justified under these circumstances whether the demonstrator is a grandmother or a militant young man."
Wednesday's train protest ended after about 40 minutes when police, using specialist bolt cutters, freed protester Mehdi El-Rahdi from the front of a train at the East India station, four stops from the venue.
THE ARMS TRADE
Key facts and figures from a business worth almost £19bn a year worldwide
Mr El-Rahdi, an architect from Machynllethi in Wales, had used a bicycle lock to attach himself to the train.
He was arrested and led away, shouting slogans against the arms fair.
"It's been fantastic," he told the BBC. "It's really been worth it."
During the protest DLR trains were severely disrupted, forcing many delegates to the arms fair to walk part of the way.
A second protester had chained himself to a train at Poplar station.
Liberty director Shami Chakrabarti said: "Our complaint is that Terrorism Act powers - very draconian emergency powers that were passed through Parliament with a view to being used in very extreme situations - appear to have been used possibly to quell protest."
Concerned at the blanket application of the Act across the whole of
London, she told BBC Radio 4's Today programme: "We are told by the Metropolitan Police that emergency powers under the
Terrorism Act are in force across London.
"Why are they in force without some
explanation?" she said.
"The Metropolitan Police say there is no specific threat and this is just
part of a general policy of high-visibility policing. That is unlawful.
UK DEFENCE INDUSTRY
Its biggest customer is the UK government, which last year placed orders worth £13bn
The UK is the world's second biggest arms exporter, behind the US
It claims to employ 350,000, spread over 11,000 firms
In 1999 defence spending accounted for
2.6% of GDP
"I call upon the Home Secretary, who under this legislation is required to
endorse or reject this authorisation, to explain why powers to stop people
without any suspicion of criminality are necessary across London today."
Shadow home secretary Oliver Letwin said that Terrorism Act powers should be
invoked only in genuine cases of national emergency and warned against a
"slippery slope" towards their use as part of normal policing.
He said he would raise the issue in Parliament with Home Secretary David
Blunkett, who must authorise or reject each request from a senior police officer to use the Act.
Metropolitan police deputy assistant commissioner, Andy Trotter, said he had been pleased by the success of the policing operation so far.
"We have made some arrests but the majority of protestors demonstrated lawfully and peacefully."
But he warned: "We're expecting [Wednesday] to be more challenging as we are aware of a number of groups who have expressed interest in
demonstrating at the site.
"But we have planned well for this and I'm confident we can handle any eventuality."
More than 2,600 security guards and officers are policing the site, including 25
Ministry of Defence police officers inside the exhibition centre.
The policing bill is expected to run to more than £1m, official estimates say.