The brown rat or Norway rat is the most common rat in the British Isles. It is thought to have originated in northern China. It has spread to all parts of the globe wherever humans are.
Rats are usually dark brown or dark grey and can reach 25cm (10 inches) long plus a tail of the same length. Males are larger than females. They often live underground and their holes are about 50mm (2 inches) in diameter. In gardens these will commonly be found in compost heaps under wood piles etc.