If they're that old, I'd be dubious as to their survival, Kev, but I suppose in the autumn is as good a time as any. Once you've dug the largest rootball out possible, get them planted and watered in ASAP. It might be an idea to reduce the top growth, even though you'll lose some flowers next year, possibly.

As Spritz says keep as big a rootball as you possibly can and I'd advise you to cut back the top growth hard when you move them. I would cut all branches back to 8" - 12 " high, keep well watered for at least the first year and hope for the best. They won't flower for at least one year, but they'll have a better chance of survival, long term.