The bank is being asked to invest in emerging, inherently risky clean-energy technologies, while simultaneously making a satisfactory return on the initial £3bn ($4.8bn) the government has seeded it with.

But the Edinburgh-based bank cannot afford to be too circumspect in choosing its investments. The initial funds are intended to cover only the next three years — and not getting the money out of the door quickly enough would be seen in almost as damning a light as investing it injudiciously.

Robert