Do I need to cut back my Lavatera after flowering?

[Slublu]

I've got a Lavatera Barnsley which has been flowering its socks off for a while now. I've been deadheading the spent blooms, but I now I have the odd stem on which all the flowers have finished. If I cut these back now would I encourage more flowers, or should I leave these as they are until the spring?

According to the RHS website, they are pruning group 6 which is to cut back in spring.

My mum always says never cut till spring as the old blooms help protect it against the cold weather.

Thank you both so much!