The London Traynebands were militias from the London area. They were present from the start of the war, and, whilst never being a crack fighting force (like today's equivalent), were devoted to the Parliamentary cause throughout the three wars, being present at Turnham Green, Gloucester, Newbury, and many other places.
In January 1642, all of the London Traynebands were put under the command of Philip Skippon. When asked to report by the king, in the May of that year, Skippon stated his devotion to God, and to no man, so sided with the Puritan Parliamentarians.
Skippon had a successful and illustrious career in the war, and was eventually appointed as the first Sergeant Major General of the New Model Army.