Five people have been arrested in connection with a suspected plot to use explosives made from fireworks to disrupt the G20 summit.

The three men, aged 25, 19 and 16, and two women, both 20, all live in Plymouth and the surrounding area. They are political activists unaffiliated to any terrorist organisation, and were arrested at addresses in Plymouth. They are being held under terrorism legislation. The explosive devices were made from simple fireworks, police said.

Police are targeting thousands of political campaigners in surveillance operations and storing their details on a database for at least seven years, an investigation by the Guardian can reveal.

Photographs, names and video ­footage of people attending protests are ­routinely obtained by surveillance units and stored on an “intelligence system”. The ­Metropolitan police, which has ­pioneered surveillance at demonstrations and advises other forces on the tactic, stores details of protesters on Crimint, the general database used daily by all police staff to catalogue criminal intelligence. It lists campaigners by name, allowing police to search which demonstrations or political meetings individuals have attended.

The House of Lords report on Britain’s surveillance society is a devastating analysis of the systems that have been installed by the authoritarian Labour government and the controlling forces emerging in local government. There is no question now that Britain’s free society is under threat, and it is time for the public and opposition parties to declare an end to this regime of intrusion.

Governments across Europe declared states of emergency and ordered factories to close as Russia cut all gas supplies through Ukraine yesterday in their worsening dispute over unpaid bills.

José Manuel Barroso, the European Commission President, accused the two countries of taking the EU’s energy supply “hostage” amid a cold snap across the Continent, and urged them to reopen the pipelines immediately.

Schools and factories were closed and trees were felled to keep home fires burning after Russia turned off the gas taps to more than a dozen countries. It was a clear demonstration of the dependence of the Continent on Russian gas supplies.

German exports and industrial orders have both plunged at the steepest rate since modern records began and Spain’s unemployment has surged above three million, capping one of the most disastrous days for Europe’s economy since the Second World War.

Joaquin Almunia, the European economics commissioner, warned that the picture would turn “dramatically worse” this year. The eurozone’s confidence index collapsed from 74.9 to 67.1, the lowest since Brussels started collecting the data in 1985.