Meaning of 'tunnel' and 'aqueduct'

SSE built a hydroelectric scheme in Scotland at a cost of £300m including rectification works. The company claimed capital allowances amounting to £260m on items of plant under CAA 2001 s 11. HMRC accepted only £34m and refused the rest on the basis they were disqualified under s 21 and s 22. The First-tier Tribunal allowed the taxpayer’s appeal. After the Upper Tribunal dismissed its appeal HMRC took the case to the Court of Appeal which allowed the appeal in relation to parts of the Upper Tribunal's decision but otherwise dismissed HMRC's appeal. HMRC appealed to the Supreme Court and SSE cross-appealed.

The issue before the court was whether items constructed for the collection and transmission of water to through and from the hydro-electric power station were a ‘tunnel’ or an ‘aqueduct’ within the meaning of those words as used in s 22 list...