Britain's security agencies and anti-terror police are monitoring around 3,000 UK-based extremists of dreaded Islamic state militant group, ready to carry out attacks in the county, according to media reports.

British men and women, many in their teens, are being radicalised to the point of violence within weeks, security sources told 'The Times'.

Although more than half of Islamists on terrorist watch lists live in London, especially in the capital's east and west, there are other hotspots in the southeast, West Midlands and Manchester, the paper reported.