He was knighted in 1949, and died on 15 July 1951, the day before his wife Lady Margaret MacColl was due to perform the formal opening of the Tummel hydro-electric power scheme.

Both of his grandparents died on the same day during the flu epidemic of 1895, at which point his mother married a building contractor named William Barlas.

[1] As his step-father was not prepared to fund his higher education, he began serving an apprenticeship in 1896, working for the shipbuilders John Brown and Company, of Clydebank.

The horse-drawn system was electrified in 1901, and MacColl was initially a substation chargeman, but his manager soon realised that he showed promise, and he moved first to the Test Room and then to Pinkstone Power Station.

He decided that a run-of-river system, which did not need a dam or reservoir, would be suitable for the location, and ensured that the buildings would blend into the countryside.

The Technical Development Committee visited the site in 1937, and called for a scaled-down scheme, where dams and aqueducts would be used to significantly increase the catchment area of Loch Sloy, enabling the number of pumps to be reduced to four, but even this was deemed to be uneconomic, and MacColl was told to abandon it.

His report reflected his attention to detail, with pages of statistics, maps and figures, but it was dismissed by the Central Electricity Board.

MacColl gave evidence to the Cooper Committee, particularly on how a bill for the development of hydro-electric power in Scotland should be structured, and how the Board to oversee the work should operate.

[8][9] The final report recommended the creation of the North of Scotland Hydro-Electric Board, and was welcomed by Evan Barron, editor of the Inverness Courier, as the culmination of 25 years of campaigning for the water resources of the Highlands to be used for the benefit of those who lived there.

[11] MacColl started working for the new Board in January 1944, and used his expertise at creating new organisations by recruiting a small team of enthusiastic young engineers.

Angus Fenton became the chief civil and hydraulic engineer, and like MacColl, was fanatical about hydro-electric power and was a driver of men.

[12] Before he took up office, MacColl had asked five senior consulting engineers to meet him in Edinburgh to discuss the best way forward for the fledgling Board.

Those with civil engineering expertise were William Halcrow, James Williamson, with whom he had worked on his submission to the Hilleary Committee, and J Guthrie Brown of Sir Alexander Gibb & Partners.

[12] The Panel of Technical Advisers met in October 1943, and quickly realised that MacColl's intention was to be generating electricity much sooner than anyone imagined.

Having previously produced his report for the Hilleary Committee, MacColl listed 102 sites that might be suitable, and completed the task in only three months.

[15] Several formal objections to the Loch Sloy scheme were raised, and a bitter public enquiry was held in Edinburgh, which lasted six days.

While most of the board had been rattled by the public enqiry for Sloy, MacColl argued that they should push on immediately, to ensure that the principles of the 1943 Act were upheld.

The Secretary of State for Scotland, Tom Johnston, appointed a tribunal to consider the objections, with John Camerson supported by Sir Robert Bryce Walker and Major G H M Brown Lindsay.

They noted the effects of weathering on concrete, and MacColl then asked Shearer to draw up a list of locations where Highland stone could be obtained by contractors for the various schemes.