Thanks for your responses and sound advice.
I do mulch every spring and the tree hasn't caused problems before but you may be right Dove, since the Acer has really grown this year, and thickend out, reducing the water content in the soil even further.
I will also feed it since i think I missed the blood fish and bone earlier in the year.
I feel like making more of these for a larger spread so perhaps I will divide in July/August ? I read this was the correct time to do it, and replant new pieces in well rotted compost. I save my best stuff for the roses, hostas and Clematis and I just emptied a whole compost bin into a spare 70litre bag