Yep, as has been said, report to your local PRoW officer and double-check its status.
Ploughing - Cross-field Footpath / Bridleway ploughing must be reinstated within 14 days (then 24 hours for any further disturbance). Field edge Public Rights of Way and cross-field Byways should never be ploughed. Reinstatement means restoring to 1m for Footpaths and 2m for Bridleways.
Crops - The occupier has to make sure that the line on the ground of the Public Right of Way is indicated to not less than 1m and 2m as above.
Locked gates - They can't do this.
Overgrowth - Across the path from the side = Landowner / occupier, from the ground = council.
As mentioned above, you can carry secateurs to cut back vegetation which impedes progress along a path. If blocked, you can move branches / etc and even make a short deviation from the RoW to get around an illegal obstruction. As for bolt-cutters? I've seen walkers carry them
CG, its a shame your early offers weren't taken up. Give them another ring and see if they'd still be interested. It could be though they aren't set up to take on volunteers (like me, unfortunately).
Shout if anyone needs more info.