Any desk in the city would take an Msc from LSE, Warwick and Imperial over CASS. Thats not to say that CASS isn't good - its decent. But CVs which work their way our desk are filtered / sorted by Uni, and CASS is in the 'other' pile.
Also, the Msc route will only allow you to get in through the general graduate analyst pool. For Associate hire, you need an MBA.
[MENTION=135401]BudMarsh[/MENTION]....
If you do want to get into Banking, you have to have a set idea of what you want to do. Back Office and Front Office, or Consultancy are not comparable. To get into back office, you just about need to have a Degree. It is not difficult at all. Being from a Big 4 background, you are probably over qualified.
If you do want to move away from accounting and into Banking, the Msc is an option. An Msc from LSE/Oxbridge/Imperial/Warwick, coupled with your experience will get you an interview at a few banks.
Your other route is the MBA one. Again, an MBA from a decent business school - LBS, Insead, Harvard, Wharton, etc will get you an interview.
Your other option is to stay in the Big 4 firm that you are in. Become a qualified ACA, and then look to move to a boutique Corportae Finance firm / Private Equity firm. However, the fact that it is Big 4 from Pak may hamper you.