My understanding is:
Any extrapolation on erosion would only be valid for equine access – and would probably need expert witness input on the particular path design and construction etc. So in terms of MTB access there is no direct impact.
The appeal overturned the Sheriffs original decision as it appeared that he had relied on an interpretation of the expert witness report which may have been invalid – specifically that erosion would only be problematic if relatively high use of the path was made by horses, when even limited horses using the path would have a cumulative effect especially if used in periods of poor weather. Such access would not be considered responsible. Extrapolation to MTB access would require a case-by-case investigation to consider how MTBs would impact on erosion on that particular path – and whether that would happen with light usage in good weather also. I think most people would not want MTBs to cause excessive erosion and so would recognize that doing so is not responsible access.
Digging through the legalese I think the appeal also decided that it is not illegal to put physical barriers in place with main purpose to prevent or discourage irresponsible access even if that may have a consequential impact on people who wish to make responsible access. That potentially has more impact on MTBs as putting fences and signs up to restrict access may be legal if the main purpose is to prevent irresponsible access?
What is not clear to me from this case was if I had one horse and took it up there once a year on a dry day when my erosion was minimised would I be breaking the law if I used the path (my hypothetical horse is very good at jumping gates)? If I followed the logic correctly – there was no argument that a single horse on a single occasion in good conditions would cause damage and therefore be irresponsible access – so presumably responsible access, even by horse, is still a right?
I am quite impressed that Highland Council sought to take this test case as far as this. Do they have any right of appeal, or is this case now finalised?
Whilst it may seem fair that the landowner had made alternative provision to cross his land by other paths, to my mind the Act is not about a right to transit land it is about a right to roam. If provision of an alternate route were of itself sufficient defense – that would be very bad for cycle (especially MTB) access – use the road rather than the nice single track.