I thought you might be in the UK from the description of the weather - yes, it has been exceptionally warm and sunny for a few weeks, warmer than Spain, then this week, temperatures dropped by over ten degrees C even here in the south, with lots of wind and, in some parts, plenty of rain. Those leaves on your Acer will have opened up during the very warm weather, and yes, they will have felt the shock of the sudden and dramatic change in temperature, particularly at night and if you're north of Watford. However, it might also be that the pot isn't large enough for the roots any more, so it's worth turning it out and just checking whether its rootbound or not - if it is, a bigger pot is called for. If it does need repotting, use John Innes No 3 instead of multi purpose to fill in round the rootball, and take the opportunity to inspect what root material is visible for signs of rot or infection. Because the weather's been so random, that's hopefully the cause of the problems you're seeing, because the other possibility of verticillium wilt is much worse, but time will tell.
If it remains cold and you get heavy frost at night, you might find the new leaves shrivel and drop off, and it might be necessary later to prune back the top to encourage new growth if it dies back, but see how it progresses. Live wood on Acers should not be pruned at this time of year because of the risk of excessive bleeding, so best to wait and see what happens - if the top stems die back, you can then cut them back to live wood.