Watch: Keeping guns off London's streetspublished at 14:49
Nick Beake
Home affairs correspondent, BBC London
TheMetropolitan Police, externalhas said "we will do all we can to stop terrorists getting hold of guns" in the wake of the Paris attacks.
Most guns in London are held by criminal gangs, but there are concerns extremists are looking to arm themselves with the most powerful of weapons.
I spoke to Det Ch Jo Chilton, the head of the National Ballistics Intelligence Service, Assistant Commissioner Neil Basu from the UK Counter-Terrorism Policing Network and Martin Parker form the National Ballistics Intelligence Service.