Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
There are many organizations that will take in retired horses but you will have ot seek them out. You can do this by calling all of the animal organizations in your area and even out of your area in larger cities. There are organizations that are funded privately to take in retired horses. In teh states, there are many but I am not clear about the UK. You will have to do some red\search. I found this LINK and there are many others.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, Dr. Loretta