Considering their main operations are at SEN, it would make sense to operate to that 1 LON airport. LHR/LGW would be too expensive for the limited pax numbers they'd put through
Though i agree, small pax flights to other big hubs (DUB/AMS/CDG/FRA) might be a worthwhile venture to improve the utilisation of the airport. If they were more serious about that, they'd make a bigger terminal