Personally, I don't think pay cuts are going to be on the cards: industrial relations are too poor to stomach them. Nor do I think there are going to be cuts in front-line staff (C-in and CC) because the firm's currently recruiting for both those areas...
No, the cuts will come from elsewhere. Remember that the pensions mountain is insurmountable as it is, so reduced staff costs (ergo reduced company pensions contributions) are a pre-cursor to dealing with that.
The figure of 5,000 won't all be actual jobs - it'll be MPE. So no overtime, and redistributing existing jobs elsewhere. So if (say) Finance needs to lose 100 MPE then 50 people moving to Marketing could do the trick.
I think the question is rather... Why did Future Size and Shape (part 1) when we were promised "This'll be the end of the job cuts" turn out not to be true? It doesn't bode well for trust.