The system of rail transport was invented in England and Wales, so the United Kingdom has the oldest railway network in the world. It was built mostly during the Victorian era. At the heart of the network are five long distance main lines which radiate from London to the major cities and secondary population centres with dense commuter networks within the regions. The newest part of the network connects London to the Channel Tunnel from St Pancras station. The British Rail network is part privatised, with privately owned train operating companies providing service along particular lines or regions, whilst the tracks, signals and stations are owned by a Government controlled company called Network Rail. In Northern Ireland the NI Railways is the national railway. The system of underground railways in London, known as the Tube, has been copied by many other cities.