Just to add my bit, I worked in IT in City for 14 years, and although I had an IT qualification, alot of what I studied I didn't use in my job, but it got me in the door!
There were people of all types, your wide boy essex types and top graduates both who knew there stuff either self taught or qualified.
Where I worked when times were tough the contractors where first to go or get reduced rates and alot city jobs are financed related and in these times I bet things are going to be tight.
Also, bear in mind living in London or fringes is expensive or if you live outside you will have to commute in, but you do get inner london allowance hopefully to cover some of extra living cost.
Also, financial IT jobs aren't your normal 9-5 job, they are 24hr 7 day operations, well mine wasn't and you could be required to support overnight and do weekend work, for which are rewarded, but depends what you want!
I'm enjoyed my time in the City, great place to work, but now enjoying a bit more free time!