The Defence Secretary says the changes will save £240 million a year in running costs as soldiers are moved into "clusters" in key locations. Returning forces will mainly be stationed around Salisbury Plain, Edinburgh and Leuchars, Catterick, Aldershot, Colchester, Stafford and the East Midlands.
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The Prime Minister will say Moscow's brazen flouting of international law represents a threat to the basis of democracy across Europe.
In some cases, victims of violence and other serious crimes face long delays as forces are unable to dispatch officers promptly.