Hiya thanks a lot for the responses - it's good to know and a bit of a relief actually! I, and MANY others, have rung the RSPCA and the council. Thing is, despite being picketed, the owners come out everyday and fill their water buckets and give them hay. And I think it is a privately owned field with a public path through - trying to get an answer is pretty darn hard.
It's still pretty heartbreaking though. They have no enrichment, are in an open field during the hottest weather and the coldest (I know they don't need pampering but it has to be uncomfortable sometimes, especially in the heat with no escape from the sun?). When some do break free they not only charge people but they terrorize each other. When I was little (10years) I'd often go out and take carrots to them. Now, however there must be over 25 horses, sometimes more and they are pretty dangerous.
Lastly, it has been affirmed that they belong to "pikeys" (please don't take this offensively, its just how they are known and I don't know how else to call). It's pretty well known that in this area you do NOT get involved, and that even includes the police. The only thing I wish I could do was refill their water buckets as they knock them over and then have nothing until their owner turns up again.