Because he has planning permission does not necessarily mean that he is not going to be in breach of this covenant.
This is not a matter for the local authority or the local government ombudsman. They will not get involved with regard to any restrictive covenants on the land. They are only involved with the planning consent. They will not consider those covenants.
Assuming that he has not started the work, you can apply to court for an injunction to stop the work and make him change the plans so that this access is not obstructed. If he doesn’t, it would be for the court to decide whether what he’s doing breaches the covenant.
If he has already started the work, you need to act really quickly to get the work suspended although the threat coming from the solicitor of court action and legal costs might do the trick without the need to go to court.
31 inches, 780 mm is the width of a normal door in a house and it’s highly likely that and wheelbarrow bicycle would go through that gap.
So you want get a temporary injunction to stop the building work pending the decision as to whether what he is doing is breaching the covenant.
If there are 2 of the houses affected by this, try to get the others to join in the action instructing solicitors so that the costs and risks are divided three ways.
However, if the other 2 do not want to get involved, they will still get the benefit of the legal result without risk.
Check your house insurance to see if you have legal expenses that would pay for the legal costs.
Can I clarify anything for you?
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It would depend whether the neighbour defended the application or not. The court application fee itself is not expensive, just a few hundred pounds.
If solicitors are dealing with it for you, they will charge £200 per hour including VAT or thereabouts.
If the other side are using solicitors, they will have the same kind of cost.
Fully defended hearing like this, could easily relieve the loser of £10,000 if solicitors are used to know solicitors are used, the costs would be hundreds.
I just measured the internal doorways of my house and they are 735 mm and the external door is 770 mm.
Something like this https://www.google.co.uk/search?q=wheelchair+dimensions&espv=2&biw=1680&bih=925&tbm=isch&imgil=3shuM-sEa0AxvM%253A%253BU-Wyb3It8wthrM%253Bhttp%25253A%25252F%25252Fbandageer.info%25252Fdimensions-of-a-wheelchair%25252F&source=iu&pf=m&fir=3shuM-sEa0AxvM%253A%252CU-Wyb3It8wthrM%252C_&usg=__yxIBwckHDbDj6GnrkX7mwJePuqA%3D&ved=0ahUKEwiirbDR2PLNAhVIHxoKHUFyAcgQyjcINg&ei=M2KHV-LHFci-aMHkhcAM#imgrc=3shuM-sEa0AxvM%3A
may help you if ever this gets to court.