despite being excellent and highly detailed It wasn't instantly obvious@SUNRAY has understood the current situation differently to me, I understood it as both the switch drops went to the 2 gang switch, and then there were two 3cores wired conversion method to 2 gangs of the 3 gang switch that he wanted to use the remaining switch for an outside light. Rather than one switch drop to each end, I think hes right looking at the pictures of the existing, but I was trying to understand original drawing