money, the canal company obtained a new Act of Parliament in 1806 to raise additional finance and allow an extra toll for using the tunnel. In 1807, Thomas Telford was asked for his advice. He produced a plan, which was followed until the work was completed. On 9 June 1809, both ends of the tunnel met. On 10 December 1810, the first boat passed through. On 26 March 1811, the tunnel was complete and a grand opening ceremony was held on 4 April; a party of invited guests, followed by several working boats, entered the tunnel at Diggle and completed the journey to Marsden in one hour and forty minutes. The tunnel had cost £160,000, making it the most expensive canal tunnel to have been built in Britain. It was also the longest, deepest and highest. The tunnel was long, underground at its deepest point, and above sea level. It was extended at the Marsden end in 1822 by when Tunnel End Reservoir's overflow was diverted over the tunnel mouth. The tunnel was also extended at the Diggle end in 1893 by to accommodate the 1894 rail tunnel. The extensions made the tunnel long. A survey carried out before restoration using a modern measuring system gave the length as , which is the accepted figure. Operation When the tunnel opened, the canal became a through route, 13 years after the rest of the canal had been completed and 17 years after work began, at a total cost of £123,803. Despite multiple problems, its construction showed that the technique of quantity surveying had advanced. Telford's plan covered every eventuality and was followed until the canal opened. Between 1811 and 1840, the tunnel was used on average by 40 boats daily. The tunnel is brick-lined in some places, though some sections of bare rock were left exposed. The tunnel is only wide enough for one narrowboat for much of its length and, to save on cost, a towpath was not provided. Canal boats were horse-drawn when it opened and the boats were legged through the tunnel – one or more boatmen lay on the cargo and pushed against the roof or walls of the tunnel with their legs. Professional leggers were paid one shilling and sixpence for working a boat through the tunnel, which took one hour and twenty minutes for an empty boat and three hours with a full load. The