Sorry, Eless! I hit the wrong button, and now I can't seem to get rid of my misplaced comment. I would help if I could, but my pruning times are completely different than yours.

I found this elsewhere

While establishing an Acer palmatum the plant should be staked to provide it with additional support and pruned to remove any badly placed or crossing stems. Once established pruning should be kept to the bare minimum – only removing dead, damaged, diseased and crossing stems.

Any pruning should be done in winter when the tree is completely dormant. If done at any other time the plant will ‘bleed’ sap and be weakened as a result. Minor pruning of thin stems could be undertaken in late summer or early autumn if necessary.

The timing is OK for pruning your acers, Elles, but I would only do this out of necessity. I would only prune if bits of the acer were interfering with other things in the garden. Go lightly or you will spoil the shape of the acer.

Thanks everyone. The Acers are in the way of a proposed extension and ideally they need to be moved but I'm just not physically caple of doing that. Also, as they are over 8ft tall, I'm not sure they would survive, but I need to cut off some lower branches, as I fear they will get broken off during the building work. If left they will be too close to the windows.

Elless just how near to the extension will the acers be? An 8 foot high tree is going to have a considerable root system.

The main stem will be about 6ft from the footings but the lower branches of one will be 2-3ft from a french door. I was hoping to make them more of a tree than a bush shape. I really did want to move them both but it would be too big a job for me. My OH has just finished his third course of chemotherapy and is unable to help at the moment.
I think I'm just going to have to take a chance as these lower branches will almost certainly get damaged whilst work is in progress anyway, as builders are not usually sympathetic to anything that gets in their way whilst working.

I think you will find that the roots will get damaged when they are putting the footings in, it really isn't advisable to have them so close to the extension. Is there no one you can ask to help you move them?

Thanks Moon growe, unfortunately not. My only choices really are to leave the acers as they are and hope for the best or prune lower branches and hope for the best.
To be fair, the garden, although it's my sanctury, is fairly low down my list of priorities at the moment. Building isn't due to start until summer but I didn't want to leave it too late to prune.
If OH doesn't feel any better by then, extension may not go ahead which doesn't really help in decision making.

Oh dear wish we were near enough to help you... how about putting out a plea on GoY for help to move the acers?

Aaw! That's really kind Moon growe.
I'm going to prune the lower branches and hope for the best. Moving the acers would be such a major job. Finding somewhere else suitable for them in a NE facing garden wouldn't be easy either. The are well protected from the wind where they are and are also behind a retaining wall, so that might help to protect the roots from disturbance.
I'm trying to stay positive :)