De Facto, In the example above LGW is not your alternate it is in fact your destination 2 hence it needing an alternate unless less than 6 hours etc.
EASA OPS AMC1 CAT.OP.MPA.150(b) (b) details the procedure and, as mentioned by SR-22 it is different from the Fuel En-Route Alternate procedure which can be found at AMC2 CAT.OP.MPA.150(b)