Perhaps the bottleneck could be addressed by longer opening hours at crematoria with shift working. Would allow better productivity and early evening funerals might be easier to get to for working age mourners. No doubt local authority unions would shy away from any such idea
3 weeks in England to get a slot at a crem.
3 days in Scotland to get a slot at a crem.
England has seen a massive growth in population over the last few decades whilst Scotland hasn’t.
I like the idea of evening funerals, but I’d struggle to see how they’d help. You’d need more staff to run them in the evening, and mor importantly, who wants and evening service?