There are millions of horses across England, and many more abroad. These beautiful creatures (who mostly enjoy company of other horses and donkeys) often are seen in fields, when not stabled at night. For horses abroad, we can help by avoiding supporting any kind of entertainment using horses (that includes horse racing in England, which has many welfare issues) and if you take HRT medicine, ask your doctor to not use brands that are made from urine of chained horses with their foals killed).
If you keep horses here in England, do an inventory of your paddock and stable to prevent horse theft, and ensure you have the proper time and finances to keep horses, before adopting or fostering. You can report concerns (or get advice) at World Horse Welfare.
Many children in England care for and ride horses. Gift a good book on horse care (also good for adults to read) that covers safety, feeding, grooming, bathing, tack cleaning and fair aid. Just imagine if every horse guardian owned a copy of this book, it could prevent so many issues.
One issue that is often upsetting is seeing tethered horses near roundabouts and on small roads. This is often a common practice within travelling communities, who don’t own land, so wish their horses to graze. As long as the horses have water and are regularly moved, this is unfortunately legal. However you can still report concerns to RSPCA. What is more helpful is likely finding local people with land, to offer it to those who resort to such measures, rather than making judgements.