By Alistair Bunkall, Sky News
The former chief of MI6 has warned that anyone insulting Islam can expect to provoke a reaction and that "there will be another terrorist attack in this country."
Sir John Sawers was delivering his first speech since leaving office. He stepped down as 'C' in November 2014 after five years at the helm of the Secret Intelligence Service.
Sir John picked up on comments made by the Pope in reference to the provocative cartoons published in the French satirical magazine Charlie Hebdo, where 12 were killed in a terror attack. Al Qaeda said the attacks were revenge for the depiction of Mohammed.
Pope Francis told crowds in The Philippines that a friend who had cursed his mother could "expect a punch" in return.
Sir John said: "There is a requirement for restraint from those of us in the West.
"I rather agree with the Pope that, of course, the attacks in Paris were completely unacceptable and cannot be justified on any basis whatsoever, but I think respect for other people's religion is also an important part of this.
"If you show disrespect for others' core values then you are going to provoke an angry response. That doesn't justify anything, but I think we just need to bear it in mind."
Sir John praised the work of the intelligence and security agencies but reiterated the threat to the UK from terrorists: "If I was to sit here and say will the goalkeepers of the security services and the police keep every single attempt to get the ball into the net, out? No. At some point these threats will get through and there will be another terrorist attack in this country."
Sir John said there cannot be any "no-go areas" either in the physical or virtual world and said there cannot be a trade-off between security and privacy.
"If the technology companies allow to be developed, areas that are simply impenetrable, you're inviting problems," he warned.