OH has faecal incontinence

Oh dear, I'm so sorry you have this to deal with. I think our generation (males and females) were largely brought up to think that cleaning up after others is women's work. I've always had a Feminist streak, right from a little girl, but it didn't stop me turning into an adult woman who automatically jumps in to help when there's mess to be dealt with!
I'm sorry but I can't think of a way for you to change things. At 90, I presume you've been married for a long time, so giving your combined responsibilities a shake-up would be very difficult now. All I can think to suggest is that you speak to your GP or district nurse. Enquire whether social services can provide some help (if only by enabling your husband to be more self-sufficient). The Citizens' Advice Bureau might have some info too. I wouldn't bother with Age UK unless you know they offer help with this kind of thing - in my area, they're really only concerned with socialising rather than helping elderly folk to live independently, but their services vary from region to region..