London, June 28 (IANS): British Home Secretary Theresa May has urged parents to report their children to police if they are at risk of becoming terrorists.

In the wake of the Tunisia atrocity, the home secretary warned it was difficult for the intelligence agencies and police to stop so-called "lone wolf" attacks by individuals radicalised online, the Daily Mail reported on Sunday.

And she revealed plans for a major counter-terror exercise to "test" the country's ability to deal with an attack on British soil, after 40 plots were disrupted in the last decade.

May is chairing a meeting to update on the latest casualties from Tunisia and hear from the heads of MI5 and MI6 on the threat posed to Britain.

Police and intelligence agencies say the "lone wolf" plots are the hardest to disrupt because they can be the work of a single person with little or no contact with known terrorists groups, the daily said.

May said it was up to friends and family of potential terrorists to spot changes in behaviour and report them to police.

She told BBC: "We want to work with families and communities. If they are seeing signs of somebody being radicalised, if they are concerned about the behaviour perhaps of their son or daughter, or perhaps of somebody's friend, that they actually are able to come forward to the authorities and talk to us about this.

"So that we can perhaps stop somebody from going down that path of radicalisation."

Ministers are increasingly worried about so-called "bedroom radicalisation", where people have been drawn to extremist ideology after watching videos on the internet, the daily said.