Basically, yes there is free motorbike parking at Stansted for local staff, but I hear it's now a bit more rigorous - the ID unit will issue you a pass if you're entitled, and cars trying to skip through the barriers to the staff car park has been clamped down upon. It was getting silly, every morning the broken barrier would be lying on the ground, from various commuters and freeloaders trying to tailgate and park for free. Dunno if non based commuters with motorbikes can avail of it, but it's worth asking.