I have at the top of the stairs an old MKG335 Switch which has 2 x L1 and 2 x L2. There are 2 pairs of wires coming into the connection which are both Black & Red, 1 of Each into L1 & L2.
The lights are on a loop with 2G 2W switch downstairs, a 1G 2W upstairs anf this one.
I have bought a...