As an ex-Banking IT Contractor...
As an ex-Barcap contractor from way-back (and ex IT contractor in banking... gave it up to have a life), this type of move is par for the course if you work in banking. The idea is during the good times, when projects are on the go, salaries go up; but as an IT contractor you know, in the back of your mind, that once the bad times happen it will be your head/salary on the chopping block. You take the higher pay, you wear the risk.
I left after 20 years in the industry. It was fun, allowed me to buy my house, but now I find that having my life back and working a government contract much better. Hours are good, so instead of leaving the house at 06:30 and getting home after 2000 I actually get to see the kids. My initial drop in salary was 20-30%, but have been able to raise my wages by 4% each year over the last two years. This year my contract was renewed for 12 months and where I work we're doing a new project, so funding is good. Change of bosses is good, with the potential for greater moral fibre (in Banking people at my level were vetted for honesty and integrity so, I suppose, we wouldn't actually compete with the Banking executives for their positions).
All in all - I understand why the banks do it (easy savings); and I understand why banking IT contractors accept it (hard to get jobs this time of year, still a good salary, may be able to make it up with extra hours); but I'm very glad to be out of it.