I'm not sure that's entirely true. I've just checked the fare from SEN, LTN and LGW to Faro for a week in October and they are nearly the same. Outbound from SEN was cheapest, while inbound to LGW was cheapest. For flights to Malaga int he same week SEN is the most expensive both outbound and inbound; LGW is the cheapest outbound and LTN the cheapest inbound.