Scotland Yard to mount one of its biggest ever operations on the day of the wedding amid fears of disruption by activists

Police across the country could make pre-emptive strikes in the coming days to arrest activists intent on causing trouble during the royal wedding, Scotland Yard has revealed.

The Metropolitan police are working with other forces across England and Wales and using local intelligence to identify activists and anarchists who they believe are committed to carrying out criminal activity on 29 April.

"We will attempt to prevent people coming to London to carry out criminal activity," said assistant commissioner Lynne Owens, head of central operations at Scotland Yard, adding there would be police activity in the days ahead of the event to "disrupt any criminal behaviour that may be anticipated".

But the tactic of making pre-emptive arrests of groups or individuals planning demonstrations is controversial. Police have to prove that a criminal plot has taken place before moving in, or that a breach of the peace is imminent, for example seconds, minutes or possibly hours away, according to legal experts.

Scotland Yard has also said that two groups have applied for permission to protest in the immediate area of the wedding on the day. Muslims Against Crusades, an offshoot of the outlawed group al-Muhajiroun, is in ongoing discussions with the police. The Yard has refused them permission to demonstrate outside Westminster Abbey but cannot stop them mounting a static protest elsewhere. In response, the English Defence League has indicated they will mount a counter-demonstration, raising fears of a flashpoint on the day.

Anjem Choudary, spokesman for Muslims Against Crusades, said the group believed the royal wedding was the perfect time to mount a demonstration. "The timing on the royal wedding is absolutely spot on because it will raise awareness among the masses here and around the world that the Muslims will never remain silent," he said.

In the past, members of the group have burned poppies on the anniversary of Armistice Day and carried out demonstrations in east London against troops returning from Afghanistan.

Scotland Yard will mount one of the biggest operations in its history on the day of the wedding. Just under 5,000 officers will be deployed. Police are likely to use section 60 of the Criminal Justice Act 1996 to impose zones where officers can stop and search individuals, regardless of suspicion.

Owens said: "If anyone comes to London on the day of the royal wedding intending to commit criminal acts, we will act quickly, robustly and decisively so it is a safe and happy environment for everyone else who wishes to be here and celebrate."

She said it was a security operation and, as such, might not be compatible with the wishes of any protesters.

The police said they were getting daily intelligence updates from both covert and open sources, such as social media sites. But they admitted the tactic adopted by anarchists of creating a "black bloc", where individuals turn up at an event, cover their heads and put on black clothing to appear as a solid mass and remain anonymous, was difficult to anticipate.

The Yard said those who had committed criminal acts at previous demonstrations, including the TUC march and the anti-fees protest last year, came from all over the country.

Sixty people who have been arrested at previous demonstrations have bail conditions which ban them from entering the City of Westminster. They would be arrested if they were seen in the area on the day, the police said.

Pre-emptive action could include moving in to break up squats in London or elsewere where individuals are gathering. They could also carry out arrests under conspiracy laws if they had enough evidence that a criminal plot or conspiracy had taken place.

But Mike Schwarz, of Bindmans solicitors, said: "Both of these tactics would be very controversial, particularly with protesters, because they have rights of expression under Article 10 of the European convention on human rights and under Article 11 of assembly, and the police have an obligation to facilitate that.

"The police would have to show that what was planned was not just a demonstration but an unlawful act and that could be problematic for them."