Complex sentence: Armed Response Vehicles were introduced to the British Police to provide them with a firearms response capability, as the United Kingdom police do not routinely carry firearms on patrol, with the exception of a minority of armed officers.
Split into simpler sentences: Armed Response Vehicles were introduced to the British Police to provide them with a firearms response capability. This being, because within the United Kingdom police do not routinely carry firearms on patrol, with the exception being a minority of armed officers.