The Animal Welfare Act 2006 confers a Duty of Care on all owners and keepers of animals and prosecution may be taken against an owner or keeper not meeting the needs of an animal.

All cases of abandonment are different. 

A horse or pony may be found abandoned on a road, in a field or be abandoned whilst in livery.

As no two cases are the same, a general outline of relevant information can be found here and a sample of an Abandonment Notice can be downloaded here

It is adviseable to make contact with either the NEWC office or one of the specialist equine welfare organisations for specific advice on your individual problem.

Whatever course of action you decide to take, it is imperative to keep a paper trail and records of money spent or received, expenses incurred and actions taken (such as veterinary treatment, vaccinations, worming and so on) for several months afterwards. There will always be the remote possibility that the owner may come forward in the future wishing to reclaim the horse (if the horse has been stolen before it was abandoned, they may have spent months looking for their equine). Here the law becomes even more complex and if an agreement with the owner cannot be reached, you may need to take legal advice to resolve the situation satisfactorily.