I think the most recent example of ring-fenced client money being jeopardised is that of Beaufort Securities, who were rightly shunted into insolvency by the FCA.
The key issue in this case is the smash and grab being carried out by PwC, who initially quoted a £100m fee to wind up the business. As Beaufort were as light on assets as they were on integrity (DoJ indictment incoming), the administrators fees will have to come from somewhere… 
Though, PwC have as of last week offered close to a 50% reduction in fees (oh the benevolence!) but this hasn’t yet been agreed. Minor digression: the likely net outcome is some clients will lose money.
@nanos is absolutely right that the assertion of ring fenced money is as safe as houses (oops) is really not 100% correct but @evangelskies, to go back to your question in a round about way, Theodore makes the most important point on this when he said this:
And key to making those calls is having abundant and accurate information.
Links to the Beaufort situation below, I think this constitutes as some evidence.
[Title: Beaufort Securities’ clients in angry clashes with PwC]