The imperial Ms Finance is a great program as well. IT is pretty quantitative, which is a definite plus. However, in terms of prestige and overall reputation, LSE is by far your best choice when comes to finance. Keep in mind that admission to any of these programs is not easy at all.
I would advise you to stay away from Cass. They try to sell themselves by aggressive marketing and fancy new building, but LSE , Imperial , and HEC are all better choices.
I would suggest to do a research about Saint Gallen university in Switzerland. It has an amazing Ms Finance&Banking program, which ranks 5th in the world, according to the latest Financial time ranking.http://rankings.ft.com/businessschoolra ... ience-2012
It is basically "free" compared to the others because it takes just about 5 000 euro to complete the program, but its overall reputation and the fact that it is located in Switzerland makes it a very attractive option. Saint Gallen is considered the Harvard of the German speaking world and opens a lot of opportunities in Switzerland, Germany, and Austria.