Exclusive: As police investigate the student protest which turned on the Conservative Party headquarters, Channel 4 News obtains dramatic new footage revealing what happened inside 30 Millbank.

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Fifty people have been released on bail following yesterday's student protest which ended in violence as demonstrators stormed the Conservative Party HQ in central London, smashing windows and throwing missiles at police.

The police have launched an investigation into how officers prepared for the protest after the unexpected violence was described by Metropolitan Police Commissioner Sir Paul Stephenson as an "embarrassment to London".

Storming Millbank

Channel 4 News has exclusively obtained dramatic footage of the moment demonstrators broke through the line of outnumbered police and climbed the stairs to the roof of 30 Millbank.

On their ascent, demonstrators daubed graffiti on walls saying 'Tory scum', drenched hallways with water from a firehose and set off fire extinguishers.

Whilst on the roof, the footage, captured by independent filmmaker Luke Flegg, from Bournemouth, recorded the moment a fire extinguisher was dropped over the parapet and into the crowds below.

The chairman of the Police Federation said today that whoever threw the canister off the roof and into the crowd could face a charge of attempted murder.

Today Sir Paul said his officers had come "perilously close" to being seriously injured.

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'Outnumbered police'

Teams of Metropolitan Police officers have begun scouring footage and photographs of more than four hours of clashes outside the tower block that houses the headquarters of the Conservative Party.

Sir Paul admitted his force underestimated the number of people who would join the march and mistakenly categorised the event as a low risk to the capital.

The commissioner pledged to examine what went wrong and apologised to those left inside 30 Millbank, including senior politicians, for their "traumatic experience".

Prime Minister David Cameron called for "the full force of the law" to be used against those responsible and welcomed the announcement of a full inquiry by Sir Paul.

National Union of Students president Aaron Porter told Channel 4 News yesterday that the violence was "despicable" and said a minority of troublemakers had "hijacked" the march.

The violence was sparked as a peaceful march involving thousands of students mobilised from across Britain to demonstrate against the planned rise in university tuition fees.

Fourteen people were injured, including seven police officers, when dozens of activists stormed 30 Millbank, a tower block housing the Tories, as well as several Government agencies and private businesses.

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Independent filmmaker Luke Flegg

Luke Flegg, who captured the footage broadcast exclusively on Channel 4 News, said he hoped the good intentions of the protest wouldn’t be overshadowed by those that turned it into a riot.

"I have so much pride for students campaigning for change in education," he told Channel 4 News.

"It's really important to me that the students that went there with the right intentions are the ones who are heard as much as the troublemakers.

"The police were incredibly patient. They were very non-aggressive.

"They looked kind of pathetic, initially, particularly before the riot police came out. There was just a handful surrounded by all these students."

The filmmaker added that he didn’t think an "organised body" had colluded together deliberately with violence in mind.