Home Secretary David Blunkett has ordered police to explain why they used anti-terrorism legislation against protesters at Europe's biggest arms fair.
Some police used powers under the Act to stop and search protesters
Mr Blunkett said he had demanded a report on why anti-terror laws, instead of public order legislation, were used by some officers.
And a civil rights group is planning a legal challenge over the use of the legislation at the Defence Systems and Equipment International (DSEi) at the ExCel Centre in east London's Docklands.
Protests on Wednesday delayed the Docklands Light Rail after two demonstrators chained themselves to trains.
The arms show was also picketed by a few dozen protesters and, at one point, a mass cycle
protest of about 100 riders.
But the protests - amid more than 2,600 security guards and officers policing the event - were muted and caused no serious disruption to the event.
THE ARMS TRADE
Key facts and figures from a business worth almost £19bn a year worldwide
On Wednesday 35 people were arrested for offences ranging from breach of the peace, to highway obstruction and criminal damage, police said.
That brought the total number arrested since security operations began on 1 September to 114, Scotland Yard confirmed.
Deputy Assistant Commissioner Andy Trotter said only two people had been arrested under the terror laws.
They had been found inside the perimeter of the compound and had been acting "in a suspicious manner", he said.
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
Mr Blunkett requested an immediate report from the head of the Metropolitan Police's Counter Terrorism branch as to why the Terrorism Act 2000 had been used at all.
It "was made available for the second anniversary of the attack on the World Trade Centre... in case there were terrorist attacks or measures that we had to take to counter terrorists," he said.
He said he had asked police "why it was that they chose to use that particular part of the counter-terrorism legislation rather than wider public order legislation."
But Mr Trotter said the Act had been used "appropriately" in "exceptional circumstances".
"We are not using anti-terror legislation for the people obstructing the highways, we would be using the Highways Act for that," he said.
"We are in a target-rich environment, and we have to be aware of terror threats," he said - adding that he would discuss the matter with Mr Blunkett.
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".
Liberty director Shami Chakrabarti said the terror laws were "very draconian emergency powers" to be used in "very extreme situations" - but now appeared to have been used possibly to quell protest.
Mehdi El-Rahdi, an architect from Machynlleth in Wales, was one of the protesters who attached himself to a 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."
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.