steadyasyougo:
I don't think the FSA "hardship waiver" is exactly as you describe it.
This clause refers....
"if the outcome of the test case produces a result that is more favourable to the complainant, the firm must take all reasonable steps to pay any difference in the amount of compensation actually received by the complainant and that that the complainant would have been entitled if his claim has not been settled by the firm then;"
In particular, it' not a requirement to "refund" when hardship is recognised, it' a requirement to consider the claim. Until the charges case concludes to the benefit of customers its not possible to be certain there will be any refunds however likely it seems. More importantly any decision on what size of charge is reasonable won't be decided until after the case, so without knowing the details of your claim I don't know whether your £1200 claim is reasonable.
That said the bank's interim offer doesn't seem to be very generous. Things the bank may be considering are how long have you been in hardship for and to what extent are you struggling to meet your bills. If you still bank with them they may have a shrewd idea (unfortunately).
Google for "bank charges refund hardship" and follow up any likely looking links. In effect you are in a negotiating position and you have the bank's opening offer. That's all. Up to you how you respond. If it's any help RBS have reduced their Unpaid Item Fee from £38 to £5 which may be their view of which way the wind is blowing on reasonableness.
Careful what you sign but an interim award now should not affect a future payout.