Just saving the slots for all the BACon pilots when BACon goes under!
Not exactly! BA at Gatwick is at present converting to "Mid-Fleet" whereby Short Haul (SHAG) and Long Haul ops will be combined. Ultimately, the BA offering at Gatwick will be substantially different from that offered at Heathrow (maybe akin to the BA Connect brand if it is successful!) Of course, if BA Connect is too successful, BA will probably sell it (remember Go!!!)
Those people, pilots and cabin crew, on BA Mainline contracts will (supposedly) be offered positions at Heathrow if they wish, hence the lack of available positions! Incidentally, Cabin Crew positions now are only advertised for Gatwick (and on the new contracts!!!)