So you actually have a 'forest' of tree peonies, Lazyhoe? The outer ones that have grown from self-sown seeds can just be hacked and grubbed out. Then look at what you want to keep. Stems that you want to keep can be cut down to ground level during winter and they will produce new stems next year, however these new stems do not flower in the first year of growth.
We had a tree peony that thought had been killed by the long freeze last winter. We cut it all right down to the ground and it as responded as a fine shrub with many new stems. It will flower next year.

thanks bulbaholic if i prune instead of cutting right back will i get flowers next year and how do i prune?.
I dug up all the seeded ones and gave to friends and most survived and are growing well

If you take a close look at your tree peony, Lazyhoe, you will see that each stem is bare at the bottom with leaves and the flowering heads at the top. This means that you cannot just trim off the tops to tidy it up as you will be left with bare stems. Try to identify old growth and smaller, new growth and then cut out the old stuff. This will allow the new growth to flower next year. Hope this helps.

thanks bulbaholic lazyhoe