Apples gone AWOL

First of all, if the trees were planted as one year old feathered maidens then fruiting is normally to be expected when the trees are 5 years old. If they were bigger trees when planted then they should be fruiting. SO, you are looking for other causes.
If the trees did not produce flowers at all, then the need feeding with Tonk's Formula Rose fertiliser in spring at the recommended dose, and/or if they are in grass then th grass should be removed from at least a metre diameter from the trees trunk.
If the trees produced flowers, then it is a fertilisation problem. As you say the site is windy then and at the seaside, so it might well be that bees are not able to work in the prevailing conditions in spring. That is much harder to deal with as erecting some sort of shelter belt on the windward side could be difficult. Frost at sea level should not be a problem. however apples and pears do need a cold winter period to ripen the wood on which flowers are produced.
If the flowers were fertilised and the fruitlets subsequently dropped off then again, that is likely to be a wind/salt problem.
Sorry not to be much more use than that.

Hi Palustris,

Thanks for the info - that's soooooo helpful! I'm going to let her know your thoughts and hopefully she should be able to work out what the problem is. I think that they were very young trees when she got them, so I'm guessing that it could be your initial theory that they are too young.

I'll pass the info on and see what she says! I'll let you know...

Thanks once again - brill advice for trouble shooting!