im not very good as ive not been gardening too long apart from my dahlias and fuchsias but your acers to me seem to be suffering from wind burn i remember seeing a item about this on gardeners world

Yes I agree they also don't like being in sun better in shade.

I keep mine in the shade now as I find the sun just crisps up the leaves also they are sheltered from harsh winds too, mine are lovely this year. They are in pots of coarse. Hope you can move yours to the shade some day soon. :o)) I will add a picture to My Pics soon as I have taken some ;o)

Thanks for your feedback, but i find that pretty hard to believe. Behind that specific Acer there are 2 more in the middle of the main lawn which are not suffering the same effects. Also the tree has been in that position for over 7 years so why all of a sudden has it decided to decline...Thought it might be some sort of leaf disease/ or virus ???

I would remove the tree just in case it is diseased.

this doesn't look like a Japanese palmatum type of Maple to me anyway, in which case, exposure to sun and wind isn't a problem. I'd be concerned about Verticillium Wilts though - these trees are prone to this, and if its that, it should be removed immediately, together with all roots, and replanting of an Acer in the same spot should be avoided (along with Berberis, Sumach, daphne, quince, any of the prunus group, Catalpa, Judas tree and Cotinus. Equally with phytopthera, it should be removed - check the base of the stem for signs of damage or rot, remove some bark near the base to see if there's any discoloration in the vascular tissue such as purple brown streaks - if there are, that would confirm Verticillium.