I transferred my acer into a new pot three weeks back. The plant looked fine until early this week when there were a couple of frosty mornings and strong winds from Storm Hannah. The newly opened leaves wilted and dropped off. The young shoots and branches are now drooping. It might also be over watering but I'm unsure. What is the likelihood of the plant growing again now that I have moved it into a bigger pot with new ericaceous compose and have allowed the soil to dry out. Any advice given will be gratefully received. Thanks so much.
Since you mentioned storm Hannah I assume you are in the UK.
Acer palmatum is very frost hardy, except that late frosts can damage new leaves, which is what seems to have happened to yours. This can be a problem with container grown plants if you try too hard to protect them from winter weather and they start to grow too early in spring. Temperatures down to -20C won't kill it if it is dormant for the winter. In the wild, they grow on mountains at altitudes of 3000-4000 feet, so a bit of winter cold isn't going to finish them off.
Just give it a normal amount of water, and wait. It will probably grow a new crop of leaves this spring.
Don't forget it's a tree. In the wild, it will just take everything the weather throws at it for 50 or 100 years without any permanent damage. Don't try too hard to be kind to it!
Letting general purpose potting compost "dry out" is never a good idea, because it can be difficult to wet it properly. If it gets really dry, water just runs through the pot instead of soaking into the compost. But with luck you haven't had enough time to reach that level of dryness yet.