Are you sure, he is not one of the cats from the nearby stable?
Ask whoever owns the stable, if you can, take a photo of the cat on your phone, and take it with you.
If you start feeding the cat, you must be prepared to go on doing so, and be prepared to deal with any illnesses or accidents he might have, unless you are hard-hearted enough to ignore that he is ill or injured, which you are not.
If you were, you would not be considering feeding him.
During the summer he can live on the mice he catches, washed down with duck food, the occasional bird, and a duckling or two! He probably won't live a long or particularly healthy life on this diet, though.
Next question: have you got close enough to him to be absolutely sure he is a he`? Otherwise you will have kittens on your hands sooner or later, and a fertile queenie cat can have seven litters in the course of a summer, with anywhere between six and eleven kittens in each litter.
If he is an adult entire male, there may be the characteristic very strong and not, even to cat lovers', pleasant smell of tom cat from his urine, but not all entire males give off this scent, and even if you do smell it, the flowering currant bush, that does not produce edible black currants but looks exactly like a black currant bush smells exactly like a tom cat!
So basically, unless you can get near enough to his rear end to see his two furry testicles, you don't know if he is a male or not (male cats keep their penis inside their body until they feel the need to air it, incidently.)
If you are prepared to keep him, well and good, but before making the decision find out whether you can legally keep a "stray" I don't live in the UK so don't know the law regarding cats there. The police or nearest animal shelter can tell you the law, or you can google it.
And find out what it would cost to have the cat neutered - there is a significant difference in the price of neutering, according to whether he is a he, or a she. Cats should also be vaccinated against cat's flu, which is a killer, and a vet will probably advise other vaccinations against contagious feline infections - there are quite a number that can be fatal.
And remember that once he is used to being your cat, you will need to find someone who will feed hm, every time you want to go away for a couple of days, on summer holidays, visit family at Christmas etc.
I love cats, but all of this has to be taken into consideration before you decide to keep one, plus the fact that he most likely catches anything that moves, so there will be dead birds, squirrels etc. to bury.
On the other hand, you and he will have hours of pleasure in each other's company, and if you want, you can restrict him to the garden rather than letting him come indoors, as long as you make sure he has somewhere warm and dry to sleep, especially in the winter and access at all times to clean drinking water.
