With respect, the daft "grade - rank equivalence" thing on MODWeb is rubbish, and in my direct experience never applied in practice.
Some of the idiots in London may think that a C2 = SO2 but this is not how it works in practice anywhere that I have worked.
Everywhere I have been (quite a few establishments) the applied equivalence has been the more realisitc one below. This has now been decreed by DPA and DLO as the equivalence levels that they apply.
C2 = Lt, Flt Lt,
C1 = Lt Cdr, Sqn Ldr, Maj
B2 = Cdr, Wg Cdr, Lt Col
B1 = Capt, Gp Capt, Col
1* etc and upwards follow same ranks as the mil.
As for allowances, they are not great for civvies. If you are lucky enough to be granted a Public Interest Terms transfer to the new job, then you will get some of the costs of your move of house etc paid, but will often find yourself out of pocket (I know, I've done it 4 times now).
As a new starter, then you may not be offered any relocation deal at all..............
The advice to treat all offers etc from Bath with suspicion and fight to get the best deal is all very true, in my experience if you don't press for your entitlement then you will dip out.
VP