The Islamic State terror group wants to carry out a mass casualty attack in Britain and has "no moral barrier" to using chemical weapons, a minister has warned.

Security minister Ben Wallace said there were reports of IS using chemical weapons in Syria and Iraq, where it controls large areas, and that the Moroccan authorities apprehended a cell in February which was harbouring substances that could be used to either make a bomb or a "deadly toxin".

He also pointed to a recent Europol report which warned of the chemical threat and the potential realisation of "everybody's worst fear".