The report by Sir John Vickers into how to reform banking so that we never again have to face a choice between bailing out bankers and risking a domino like collapse of the entire economy has made a number of recommendations- most prominently that retail and investment banking should be ring fenced from one another.
What a brilliant idea, in order to avoid banking crises we should ensure that all banks either do nice safe low risk retail banking (like Northern Rock for example) or engage purely in risky investment banking so there would not be a knock on effect to the wider economy if they did collapse (like Lehman Brothers).
The Roosevelt administration brought in a similar law during the Great Depression- and bank collapses continued at a rate of 1 a week throughout the 1930s.
In theory spreading risk widely (by engaging in multiple sectors) should make banks sturdier.
And in practice none of the combined banks have actually suffered the kind of collapses that sent the economy into freefall in 2008 but they are the ones we should break up it seems.
So it neither works in theory or reality but in terms of ideology it is a winner.