You could re-instate the 20,000 police officers, arm them all with automatic weapons, post one on every London street corner and what is to stop a Jihadi carrying out an attack somewhere else, say Swansea?
Father Hamel had his throat slit as he said mass in his church in Rouen, way outside of Paris.
"More police!" gets votes, as the scurrilous Corbyn has shown, but the real issue is tackling the source of the problem, i.e. radical, and often not so radical, Islam, - the enemy within.