“There is a gap in the law around the planning of mass attacks that can be just as serious [as terrorism] in their implications for communities, their impact, the devastation that they can cause and the seriousness of the crime,” she said.
“We will tighten legislation so that that is taken as seriously as terrorism.”
Cooper said the plan – which was briefly announced in March but not fleshed out until now – was for the new law to be similar to the exceptionally serious crime of preparing for acts of terrorism.
This legislation, brought in after the 2005 London bombings, is a vital counter-extremism tool that has jailed dozens of suspects.
It allows the police to arrest a terror suspect for the steps they take to prepare for an attack – such as researching a target.
But it stipulates that there must also be evidence the preparation is linked to an ideological cause, such as support of a group banned under terrorism laws.