Resisting the urge to be an a** and correct your grammar...
Put it this way, if somebody offered you a £12k salary increase right now, would you take it? Of course you would. 24% as a salary increase is pretty good going. That being said, 53k as a base salary for a Manager doesn't sound like a lot, but I guess Cap balance that out with the high flexi fund.
Do you know what the starting salary for an Accenture manager is? I can't imagine it's significantly higher than 62k. Also, do you get a flexi fund with Accenture?
In terms of brand, I wouldn't say that there is much different between ACN and Cap so I'd take the new role. Remember you aren't guaranteed promotion at ACN.