Police arrested Anjem Choudary, one of the most high-profile Islamists in Britain, and raided 19 premises including one containing a sweet shop as they investigated the alleged encouragement of terrorism.

The 47-year-old was one of nine men arrested by Scotland Yard’s counter-terrorism officers on Thursday morning.

Police gave only sparse details, but the men were arrested on suspicion of being members of a proscribed organisation, or supporting a proscribed organisation, as well as encouraging terrorism.

Choudary was a former spokesperson for the extremist or radical group al-Muhajiroun, which was banned, and which the government says then reinvented itself under various names, which were also proscribed. Choudary has always denied allegations that he has either incited or glorified acts of terrorism.

Choudary has gained publicity for statements over the years that angered some people, but which stayed on the right side of the law. He is a former lawyer and self-styled preacher and says he is an expert in Islamic or sharia law.

One of the addresses raided by police contains the Yummy Yummy sweet shop in east London. This afternoon officers answered the shop’s door and officers could be seen inside the shop.

On Thursday morning Choudary’s phone was uncharacteristically switched off and a chat group he uses to communicate his message was silent, saying it was last viewed at 5.33am.

The men arrested were aged from 22 to 51 and were all detained in London.

Scotland Yard’s counter-terrorism command had been monitoring the activities of Choudary and others for some time.

The arrests today on Thursday followed the circulation of material in recent months seemingly sympathetic with Islamic State (Isis), which has taken territory in Syria and Iraq and says it wants to establish a caliphate or fundamentalist Islamic state crossing recognised national borders.

Detectives collected material which they believed was produced by the radical successor group to al-Muhajiroun. The pattern of the content of the Islamist material reached the threshold to carrying out arrests for allegedly encouraging terrorism, officials believe.

There had been public pressure and debate as to how Choudary’s statements – considered extreme by some, and in keeping with free speech by others – did not lead to action by law enforcement.

In a recent interview Choudary refused to condemn Isis’s treatment of Western hostages. In a series of Tweets sent hours before his arrest, Choudary condemned US air strikes against Isis and other alleged extremist targets by the US in Iraq and Syria: “The Islamic State could not wish for a better rallying call for Muslims worldwide to join them than for the USA to start bombing again.”

Al-Muhajiroun disbanded in 2004, but it and its successor groups were banned in 2005 by the government in the wake of the July 2005 attacks on London.

Its influence is alleged to have continued to reverberate. A number of people convicted of terrorist linked offences have attended its events.

After 2005 a series of successor groups were set up to beat the ban, going under a series of names, from Saviour Sect and Muslims against Crusades. In 2010 another successor group called Islam4UK was also proscribed.

Choudary has said that Michael Adebolajo, who led the terrorist attack that saw the soldier Lee Rigby murdered on a London street in May 2013, had attended religious meetings he held, years before the atrocity. Adebolajo attended the meetings from 2004 to around 2011.

Some in Britain’s Muslim communities complained that Choudary was given too much air time on television and radio to promote his views, which they claimed were extreme. The groups he was a senior figure in had at best a couple of hundred followers, but their public impact was greater than their number.

Police said 19 addresses were being searched, mostly in London, including community premises as well as residential and business addresses. One address is in Stoke-on-Trent, 11 are in east London, one is in west London, one is in north-west London and five are in south London.

Neighbours said Choudary appeared to have moved out of his semi-detached home in Walthamstow, north-east London, last week and there had been significant police activity at the address over the weekend.

“The police activity was definitely last week,” said one neighbour, who declined to be named. “Police officers came round and went up the doorstep – two were walking around constantly and there were three police cars parked down the road. They were in pairs. A police car came round a few times. Later that evening I saw the light on upstairs after the police had gone.”

The neighbour added that Choudary had lived in the house for two or three years but removed some belongings last week.

“We’ve had leaflets from rightwing groups put though our door saying: ‘Do you know he lives down your street?’,” the neighbour said, adding that they were on “nodding terms” with Choudary.

Another neighbour, Derek Rayner, 70, said Choudary “kept himself to himself” but was not popular with local residents. “He hasn’t done me any harm personally and he hasn’t done his neighbours any harm, but I just don’t want him on my doorstep,” Rayner said.

On Thursday morning the property where Choudary lived was covered in scaffolding, with a number of workers leaving and entering the house. It is unclear whether Choudary has moved out of the address permanently or just until the works, which started several weeks ago, are completed.

In a statement the Met said: “These arrests and searches are part of an ongoing investigation into Islamist-related terrorism and are not in response to any immediate public safety risk.”

Those arrested in Thursday’s raids are being held at police stations in the capital.

The Met said: “Officers from the Metropolitan police service’s counter-terrorism command have arrested nine men this morning, Thursday, 25 September, on suspicion of being a member of a proscribed organisation [or] supporting a proscribed organisation contrary to section 11 and 12 of the Terrorism Act 2000 and encouraging terrorism contrary to section 1 of the Terrorism Act 2006.”