Not likely to be rain, much more likely cold - April was unseasonably warm, but May has been unseasonably cold - it may be that the burgeoning leaves are wilting having been caught between the two extremes. Give it some shelter if possible and hopefully it will recover over the next few weeks. Otherwise, check the roots for signs of pests like vine weevil and any other signs of infestation or disease on the stems.

Hi Bamboo - can you describe the symptoms & cure for 'vine weevil'??

You will find fat white grubs in the soil at the roots, though by this time of year, they've probably hatched out and gone, so look for small beetle like creatures on the plant. Biggest indication is that, when you turn the plant out of its pot, there won't be any roots left, or nowhere near as many as there should be, because the grubs have eaten them. Watered on nematode solutions are very good, but too late for spring application - if you think that's the problem, buy Nemesys and water onto the pot/s September.

Thanks for your helpful and kind replies.

I have repotted my beautiful ~Acer into a larger pot and have moved it around to the back garden which is south-facing and not such a wind-tunnel.

It has since "picked-up" with leaves opening out etc....

We have had a colder than normal winter here in North Devon, England and I think it may have been reacting to the move from a warm temperate climate of South Western France to North Devon. UK

Thanks again