You can cut them back almost to the ground, there's a chance that they will flower again this year but anyway you will get a neat mound of new leaves.

I have successfully dug out a clump and divided it into two or three bits. A quick trim for each and replant. Various times of the year, Oxonianum are sturdy plants.
As LG says, do it now and there is a good chance of another flush.

Thankyou Landgirl and Fractal. I'll do it today when it stops raining.