at the forefront of debates as to the level of regulation and public control under which transport services should be brought. Ashfield aimed for regulation that would give the existing Group protection from competition and allow it to take substantive control of the LCC's tram system; Morrison preferred full public ownership. Eventually, after several years of false starts, a bill was announced at the end of 1930 for the formation of the London Passenger Transport Board, a public corporation that would take control of the Underground Group, the Metropolitan Railway as well as all buses and trams within an area designated as the London Passenger Transport Area. The Board was a compromise – public ownership but not full nationalisation – and came into existence on 1 July 1933. On this date, the C&SLR and the other Underground companies were liquidated. Legacy The technologies of deep tube tunnelling and electric traction pioneered and proved by the C&SLR shaped the direction of subsequent underground railways built in London. The C&SLR demonstrated that an underground railway could be constructed without the need to purchase large and expensive tracts of land for the shallow cuttings of sub-surface steam operated railways. Instead, it became possible to construct a tunnel at deep level without adversely affecting conditions on the surface. The C&SLR thus encouraged the construction of a network of underground railways in London far larger than might have been the case otherwise. The size and depth of the tunnels used on the deep tube lines, including the Northern line, does have drawbacks: the tunnels have a limited loading gauge and the lines suffer from overheating in the summer. During World War II, the disused tunnels between Borough and King William Street stations were converted for use as an air-raid shelter, with entrances to the shelter at King William Street and at six sites south of the Thames (of nine planned). In the 1960s the disused tunnels were used to assist the ventilation of London Bridge station and all the entrances bar that at 9 London Bridge Street were infilled with concrete. It is now only possible to access the tunnels from Three Castles House or a passage from the Jubilee line at London Bridge. Most of the C&SLR's six original station buildings were rebuilt or modified during the improvements to the line in the 1920s or during more recent modernisations. Only the building at Kennington