Plans to build an £800m hydro power station in the Highlands have stalled.

Energy firm SSE won approval for the Coire Glas plant at Loch Lochy, north of Fort William, in 2013.

Progress has halted because of uncertainty over the financial viability of pumped hydro projects.

Coire Glas could more than double the capacity of pumped hydro in the UK, producing up to 600MW of electricity.

SSE said "a number of commercial and regulatory challenges" will have to be overcome before a final decision is made, which is unlikely to be this year.

The firm previously raised concerns about a lack of clarity over government policy regarding pumped hydro and said the market "needs a minimum level of confidence to invest".

Pumped hydro storage schemes involve two linked reservoirs at different heights.

When demand for power is low, water is pumped from the lower loch to the upper loch and stored.

Later, the water is released and allowed to flow back downhill, turning turbines and generating power when demand is high.