It took legal action against engineering contractor Hochtief which carried out tunnelling work at the site near Fort Augustus.

A rock fall in the tunnel carrying water from the scheme reservoir to the power station in August 2009 caused the hydro scheme to close just months after it had opened. Operations did not resume at the scheme until almost three years later.

A judge at the Court of Session in Edinburgh ruled that the main part of the SSE claim has failed.

Lord Woolman said: “I am satisfied that Hochtief did exercise reasonable skill and care.

“I reject SSE’s case as it depends on the accumulation and interpretation of all the data that has been obtained since the collapse. Put short, it is founded on hindsight.

“The collapse was not due to a defect that existed at take over. Accordingly, it was an employer’s risk event.”

But the judge also held that the contractor did breach obligations by not returning to repair the tunnel and said he was minded to award SSE £1m “low availability damages” - the capped limit for compensation if the hydro plant failed to achieve certain targets in the two years after completion.

An SSE spokeswoman said: “SSE is disappointed with the ruling by the Court of Session on the compensation claim relating to repair work at our Glendoe Hydro Scheme near Fort Augustus in the Highlands. We will review the decision in more detail and assess our options.”