I could be wrong but it looks like leaf scorch to me. Perhaps you watered whilst the sun was on the leaves.

Is it in pot? Certainly looks to be, if so have you got the pot raised up on feet or set in gravel to drain away excess water.

Thanks for the replies. No it is in a garden, but the weather here has been insane. Torrential rain, high winds, frost, all in just a few weeks. I am hoping it is just weather related. It has new healthy leaves emerging and the lower branches which are sheltered are unmarked.

If you've had frost that probably explains it, Acers do not like frost on their new leaves so, just sit back and see what happens over the coming weeks.