You sure can.....they don't mind thinning out every few years

.....and I would say just after flowering has finished would be the time to do this pruning.

Many thanks for replying.

Cut out the stems that have flowered right down to the base. It flowers next year on this year's new growth. There's an enormous one on some wild land adjoining our gardens & the scent wafting over is exquisite.

Thanks feverfew.It flowered earlier in the year and I pruned those so can I do the side branches now or in the autumn as it really is crowding out other plants?

If it flowered early in the year and you think it is called The Bride, then is it a Philadelphus? The Bride is an Exochorda macrantha.
Pruning is the same though, do it now so there is new growth for next years flowers.

Think you're right owdboggy ___think I got confused.Will have a go today.Thanks all for the help.