Tunnelling began in February 1972 and was completed by the end of 1974. In 1977, during construction of the stations, the name of the line was changed to the Jubilee line, to mark the Queen's Silver Jubilee that year. A construction shaft in Hays Mews north of the station was used for an electrical substation and ventilation shaft. At Green Park, the ticket hall was enlarged slightly to provide space for escalators for the new line which connect to an intermediate concourse providing interchange between the Jubilee and Victoria lines. A second flight of escalators descends to the Jubilee line platforms, which are below street level, the deepest of the three sets. Interchange between the Jubilee and Piccadilly lines was via the ticket hall. Platform walls were tiled in a deep red with black leaf patterns by June Fraser. Trial running of trains began in August 1978 and the Jubilee line opened on 1 May the next year. The line had been officially opened by Prince Charles the previous day, starting with a train journey from Green Park to Charing Cross. In 1993, to alleviate congestion, a third escalator was installed in the lower flight to replace a fixed staircase.