They have been in about 8 years

And they need moving because the Acer is deformed by being too near the fence! and the Cornus is just too big for where it is now

If you intend moving them, then now is the time. How well they transplant due to their age and/or size is another matter. Make sure they're watered well if we have another dry spring and get as big a root ball on them as you can.

As Andy j. says get as big a rootball as possible and prepare the new planting hole before you lift the trees so that they are out of the ground for as short a time as possible. Remember when replanting to plant at exactly the same depth they were before.

If your cornus is 'alba sibiricus', the red barked version, I wouldn't even move it. It is a lovely plant but I would just take out a load of the roots because within a year or two it will be large again. The divisions can then be transplanted where you want or sold or given to friends.

The so called yellow or green barked cornus sericea flaviramea is a lot less vigorous. If it is this one then I would certainly recommend dividing as you have a slight chance of losing it if you just move it. Eggs in many baskets is safer here.

Thank you all very much for the advice, yes it is the red bark one so i will do as you say and take out some of the roots.
I have been poorly and haven't ventured out into the garden since last October !!! but it was a lovely day yesterday so did a bit of tidying up at last, it was so nice to get out there ! i still have loads to do but thankfully the front overgrown jungle is now all paved so nice and tidy, but the back .... well a lot of you will already have seen the nightmare i have been battling with but i am determined this year it will be done.
thanks everyone for your advice and support xx