Thanks bernardgreen. That is a brilliant solution. I've been to our local Screwfix and the switch is on order for tomorrow. This is slightly different but close enough to the pattern I require. I would never have found it without your guidance.
These are an antique brass model from Homebase. Their own brand and made in China with no supplier address. My fault for not checking that I needed this intermediate switch. My other option is to bypass the intermediate one altogether and just leave a dummy switch.
I am replacing my hall switches and find that there is no crossover switch option available in the range we want. Is there any way of connecting without a crossover? Perhaps using a double switch 1 gang 2 way alternative in place of the crossover.