What costs can I include in an R&D tax credit claim?

“Six categories: staff costs, apportioned to time spent on R&D; externally provided workers, such as agency staff; subcontracted R&D, which qualifies at 65% for unconnected subcontractors; consumables, meaning materials used up or transformed in the work plus an apportionment of water, fuel and power; software, data licences and cloud computing used in the R&D; and payments to clinical trial volunteers.”