Wikipedia
Brake van and guard's van are terms used mainly in the UK, Australia and India for a railway vehicle equipped with a hand brake which can be applied by the guard. The equivalent North American term is caboose, but a British brake van and a caboose are very different in appearance, because the former usually has only four wheels, while the latter usually has bogies.
Many British freight trains formerly had no continuous brake so the only available brakes were those on the locomotive and the brake van. Because of this shortage of brake power, the speed was restricted to . The brake van was marshalled at the rear of the train so both portions of the train could be brought to a stand in the event of a coupling breaking.
When freight trains were fitted with continuous braking, brake vans lost their importance, and were discontinued by many railways. However, they still continue on some important railways, such as the Indian Railways, besides the heritage railways.