Tom Brake, MP for Carshalton and Wallington was among protesters not allowed to leave a cordoned zone at the G20 street demonstrations for about five hours.
Mr Brake was following the London G20 gathering as a legal observer last Thursday when violence broke out between police and protesters in Moorgate.
He was kept inside the police cordon formed to stop violent protesters from leaving, along with bystanders, peaceful protesters and even those in need of medical attention.
He said: “I was there in the crowd as an observer and it was one of the scariest experiences of my life with a large and often violent crowd surging backwards and forwards within the police cordon in response to police charges.”
In a video interview with CNN during the "siege", Mr Brake said there were significant civil liberties issues at the site of the protest.
Mr Brake said: “The police strategy of locking in all the protesters peaceful or otherwise for up to five hours, in my view, put some peaceful protesters at greater risk, as well as having serious implications for peaceful protests in the future.”
But Mr Brake also praise the work of police to stop violence during manifestations.
“On the whole, the police handled a very difficult situation very professionally.
"Having seen the way in which large scale events are handled in some countries around the world, I think we have to give credit to the Met for the way in which the vast majority of their officers behaved,” he said.
“I am pleased that some protesters who were there to cause violence were arrested and those who were pursuing a peaceful and legitimate protest were allowed to do so.
"It is always disappointing that violent protests grab headlines and the issues many legal protesters are raising get forgotten in the melee.”
The MP will now be compiling a report about police behaviour to be discussed with the commander in charge of policing in Moorgate and the Home Affairs Select Committee.
• Were you inside the cordoned area in Moorgate last Thursday? Tell us about your experience in the comments section below.