A quick update for anyone intending cycling the GGW. We opted to do the GGW footpath - as opposed to cycle path - as it's more scenic and misses out some road sections, so I assume the cycle route is okay.
The route is fine from Fort William to Laggan Locks, but this is where the 'fun' starts. The section between Laggan Locks and Laggan Bridge has seen considerable storm damage, with many trees blown down, duly covering the path, roots ripped out creating craters, etc. so unless you're a Danny Macaskill type, you'll need to stop here and there to lift your bike over the various obstacles (awkward if you've got panniers full of bivi kit). In saying that, this section is little more than a warm-up for what's to come on the next section.
Laggan Bridge to Oich Bridge up the Southeast side of Loch Oich. Depending on what type of character you are, you may view this as a great adventure or a bloody nightmare! You will need to manoeuvre bikes over, through, around and even (crawling) under fallen trees. At one point, we had to wade, knee deep, through a stream, whilst carrying/hauling the bikes because the path was impassable. Large parts of the path are flooded and then there are the inevitable punctures, (two) courtesy of pine needles/thorns. All in all, three hours to cover this five mile stretch!
With the value of hindsight... probably should've followed the cycle route.