I'm trying to decide whether its a problem with apple sawfly, or codling moth, or possibly both. Apple sawfly tunnels into immature fruits - this often causes them to drop from the tree before maturity, but sometimes the apples do remain and mature, often with scarring like a ribbon on the outside, and often the fruits are misshapen. Codling moth goes for more mature fruits, and the larvae are also inside the fruit, so really, its down to whether you noticed holes in fruits early on in the season, before the apples started maturing.

There is a pheremone trap you can use for codling moth which may be enough to prevent that problem, but if its sawfly, you need to be vigilant next year and pick off any small fruits which have a small hole inside; you can also take the precaution of spraying the tree with Westland Resolva Bugkiller seven days after petal fall, that is, 7 days after the flowers have dropped off.

Thanks B, the problem I'm pretty sure is codling moth. Presumably I can get a trap from a garden centre ? Or are there better suppliers ? I'll also get the Westland stuff, but not until the flowers have dropped off next Summer ?

Garden centre or online - if you've only got one apple tree, the pheremone trap might be enough to keep the moth at bay. The Westland stuff is for preventing apple sawfly, if you think you might have that too - and its 7 days after petal fall, no longer - the tiny fruitlets are starting to form at that point, and that's when the sawfly lays its eggs, which is why you spray then.

B,
I see Amazon have "Agralan codling moth traps and refills", which I almost bought 5 mins ago, but understand they should be installed in Feb-March. So is there no point in buying one now ?
And is there nothing to be done at the moment except throw all the ruined apples ?

Fraid so, if the whole crop is ruined. Inspect to see if you've got any sound ones - and yes, the moth pheremone traps are erected early in the spring, not now.

Thanks once again. So far half are ruined and half are good, but there're a lot left on, most of which will be coming off this week. Will keep you informed and will get the trap march time.

Er, make it February, just in case the winter's mild like last year;-))