When you say it USED to be a footpath, is it not still a footpath?
If so it is a public right of way, but on foot only (stating the blindingless obvious - but I'll get there in the end).
This means that no motor vehicles can go down there, unless one happens to be the owner of the land, or one has an easement from the landowner.
Some public footpaths (and bridleways) are positioned on land that is actually owned by someone; many are not - particularly the old ones that are historical anacronisms from a time gone by. The ones between fields with hedges each side are often like that.
So the issue is, who owns the land?
It is perfectly possible that no-one owns the land.
When the motor car came into use, many people living up footpaths and bridleways adapted to suit. Those that could get into their land did so, and in a time when people worried far less about 'rights' and 'suing', took cars up footpaths and bridleways. Having done that for 20 years without anyone complaining, those people were able to acquire an easement by prescription (using the Prescription Act 1832) for the right of passage by motor vehicle - even when the public right of way is a lower category of footpath/bridleway.