depends how far into seed production they have gone. Mine are dry and shed their seed so mine won't this year. If the flowers are just going over you may get another flush.

From what you say SBG, I think I have a couple of later flowerers that might do it. Thankyou

I have just cut mine back to soil level. I have given them a good feed and have kept them well-watered so I reckon they will flower again before the Autumn. I would certainly dead-head them anyway unless you want them coming up like weeds.

Thanks Jimmy, Ill try cutting them hard back as you have done. I would like some to self seed so I'll leave some.

I cut to the next set of leaves and they flower again but not as well as the first time

Walesgirl, that's useful to know too.
Thank you for all taking the time to answer.