Twenty people were arrested today as Scotland Yard launched dawn raids ahead of the Royal Wedding amid fears of violence tomorrow.
Officers swooped on three squats across the capital just 24 hours before William and Kate marry at Westminster Abbey.
The Metropolitan Police said the raids were carried out as part of an investigation into disturbances at the student protests last year and the recent trade union march.
However, sources told Sky News that officers had targeted people who were known troublemakers.
Labour backbencher John McDonnell accused police of carrying out 'some form of pre-emptive strike'.
A force spokesman admitted the arrests had been brought forward because of the Royal Wedding at Westminster Abbey.
Mr McDonnell accused the Metropolitan Police of a 'disproportionate' reaction to the threat as he raised a point of order in the House of Commons.
He added: 'I believe this disproportionate use of force is unacceptable and I would urge that a minister comes to this House from the Home Office to explain what is exactly happening today, what are the grounds for that action and also to contact the Metropolitan Police Commissioner to explain that many of us feel that this is disproportionate and no way to celebrate this joyous wedding.'
Officers arrested 19 people in Camberwell on suspicion of abstracting electricity and one person in Hackney on suspicion of disorder at the TUC march.
Another address in Sipson, near Heathrow, was also raided but there were no arrests.
Police had been expected to carry out a number of arrests ahead of the most expensive and high-profile security operation in a generation for Scotland Yard.
More than 5,000 officers will make up a multimillion-pound ring of steel tomorrow as the world's attentions focus on London.
Snipers will take to rooftops and undercover officers will mingle among the crowds as part of a massive covert and overt operation to avoid an atrocity.
Security against potential threats from al Qaeda-inspired extremists, dissident Irish republican terrorists, anarchists and even lone stalkers is being balanced with the desire to let onlookers enjoy the day of pageantry.
Around 70 people are now banned from the City of Westminster as part of their bail conditions after being arrested or charged over various previous alleged disorder offences.
But despite up to 80 VIPs requiring personal protection, there has been no intelligence to suggest police will need to use anti-terror powers as hundreds of thousands arrive in the capital for the event.
Police have been scouring London for explosives and hidden weapons in recent days, inspecting drains, lamp-posts and traffic lights in Westminster.
Joe Rake, 20, a Transition Heathrow campaigner who lives at one of the squats in Sipson, said he woke up to 40 officers raiding the property at dawn.
'They asked us if we had been involved in the TUC protests,' he said. 'It seems obvious to us that they thought we were going to do something at the wedding tomorrow. They searched through our things but took nothing away and made no arrests.'
The Heathrow raid was carried out in Mr McDonnell's constituency.
He told the Commons one of his constituents was handcuffed before officers 'forcibly detained another group of them in a building on the site'.
'It appears that raids like this are going on across London at the moment as some form of pre-emptive strike before the royal wedding,' he said.
A spokesman for the Metropolitan Police said: 'These arrests are part of ongoing proactive work to tackle suspected criminality.
'They are not specifically related to the Royal Wedding but have been brought forward ahead of the event.'
He added that it was an 'intelligence led operation'.
Chief Inspector Simon Turner, of the Territorial Support Group, said 'This isn't linked to the Royal Wedding.'