A Computer Science degree is a highly sought after degree for city jobs. Just to give you some examples of some of my friends (all doing computer science), many of them have got into Accenture, PA consulting and BAE systems for consulting related jobs. Some (including myself) will be doing accountancy ACA training next year and some will be going to ABN Amro, HSBC and RBS for Banking related work. You can also go into technical jobs such as one friend of mine who will be working in satellite communications next year. So on the whole a computer science degree (from a decent uni) will enable u to work in a variety of sectors, including Consulting, Accounting and Banking.
A computer science degree will provide you with teamworking skills (through the many group prj you will undertake), it shows you have good problem solving skills and can handle advanced numerical problems. And on the whole it is very favoured amongst city employers.
One piece of advice however, try to do a few mgt modules if possible as city employers do favour some knowledge of business. I personally decided to study Computer Science with Management. Imperial's MSc Computing (Computational Management) is an excellent degree so I suggest u look into that. When I had my assessment centre with PwC and Deloitte, I met more than 5 ppl doing that very exact degree - so do check up on that. On the whole however, a computer science degree is looked upon in the same light as an Economics or Maths degree and is sometimes favoured over Business Management Degrees.