Looks very much like Scab.

Thanks for your response Owdboggy. What should I do about it? How should I treat it? I'll have look in a book/on the internet, but I like to have input from someone with experience too!

We do not spray with any of the available fungicides, but if it gets too bad then Copper sulphate is a reasonably organic material.
Cannot help with any of the other fungicides sorry. Never used them.

RHS advice on this is to clear away all leaves as soon as they fall, and to prune out badly affected twigs, particularly in autumn. The fungus that causes this overwinters on the tree, on fallen leaves and fallen fruits. These should be 'burnt' although that depends where you live whether you can do that or not.
Fungal treatments that help in the UK are products containing difenoconazole (Westland Plant Rescue Fungus Control) or myclobutanil (Bayer Garden Systhane Fungus Fighter), but only if you rigidly follow the recommended timetable in the instructions. Its also important to treat the whole tree, but of course, that's not always possible with large, old trees. These treatments only control the problem, not get rid of it.

Thanks again. A last question! I have a fungicidal spray that the local GC recommended for fruit and veg which did the trick on my raspberries a couple of years ago - I will use that if necessary. If I do decide to spray, should it be done now and perhaps again at the start of next years growing season, as I do with roses.
I appreciate your advice.

Sorry, can't say because I don't know what the spray is - if it doesn't contain either of the two ingredients mentioned above, not sure it'll do anything. I also don't know what the timetable is for application of those products I mentioned - inspecting the packaging might give a clue, or maybe there's more info on line if you google the name of the sprays. I got the info from the RHS online guide to Apple Scab and treatment for it.

Thanks Bamboo. Sorry, I've only just noticed that you also replied! I can get Bayer products here so I'll also have a look at that and speak to the guy in the GC. As it's only a young tree, treating the whole thing shouldn't be too much of a problem. I'm new to fruit trees - never had them before so I think it could be that it needs a bit more pruning next time to let the air in a bit more. Is there a cure or will the tree now always have it?

You will probably always have to watch for it, and have the product handy to treat with - there are scab resistant varieties of apples on the market. Check the timetable and apply according to that. Perhaps you have a particularly vulnerable variety.

Thanks Bamboo.