I would be suprised to see BMI operating long-haul out of LGW as they have no flights there currently, as Johnnybgoode stated. It would also be a huge concession to BA and Oneworld about the flight for BMI to operate l/h from LHR. Why bother setting up ops at LGW, just to move them to LHR when they can. Expensive.
Also, BMI don't have the a/c to be setting up lots of new routes yet. I know they have another couple of A330-243's on order, but they'll need to order some more soon, surely? Maybe we'll even see some A340s for long-haul heading east? I hope so.
Their l/h service is fantastic. I would reccommend it to anyone.