FOUR QUESTIONED IN 'G20 PLOT' PROBE

Three men and one woman were arrested in Plymouth, Devon, between Friday and Sunday after police discovered imitation firearms, makeshift explosive devices and "political literature" while investigating a minor offence of criminal damage.

A fifth suspect, a woman, was released late on Monday night following a court hearing at Plymouth Magistrates' Court.

The remaining four suspects are being held at Launceston police station under the Terrorism Act.

Devon and Cornwall Police refused to confirm or deny that the arrests were connected to a plot to disrupt the G20 summit, though sources claimed the suspects planned to target the meeting of the world's most powerful political leaders in London later this week.

Forensic evidence was removed from a property in Radnor Place, Plymouth, believed to be the home of one of the suspects.

At a press conference at Crownhill police station in Plymouth, Assistant Chief Constable Paul Netherton said the investigation was sparked when a 25-year-old man was arrested for spray-painting on a wall in Plymouth city centre - but would not comment on the nature of the graffiti.

One source said the group were political activists who may have aspired to disrupt the G20 summit, but not to injure or kill.

Scotland Yard has issued warnings that protesters are planning to bring the City of London to a standstill with high-profile protests this week.

The G20 summit, which begins at the Excel arena in London's Docklands on Thursday, has been described by senior officers as the capital's most challenging police operation for a decade.