NLP
A few of the Bath Road hotels, such as the Ibis, the Arora, the Premier Inns (both the "T5" one and the Bath Road one), and the Hilton Garden Inn at Hatton Cross (formerly known as Jurys Inn - handy for the Training Centre) frequently offer discount, also there are a handful of crew B&Bs near the crew car park again just off the Bath Road.
You might want to contact those hotels direct at this stage and see if they can offer anything ahead of your joining BA/before you get ID. I'd best not put any required log-ons here - once you're "in" you may be able to find out full discount details via in company intranet/BALPA forum.