You don’t even have to ask IB. Simply go to their website and scroll to the bottom of the page. There you’ll find a description on how each subsidiary is regulated. That includes the subsidiary in the UK.
Everyone said that about Enron before it went under. And Bear Sterns before it went under. And Worldcom before it went under. And any of hundreds of other firms that unexpectedly went bankrupt. The whole point of an unexpected bankruptcy is that it's unexpected! Denial is more than just a river in Egypt.
That wasn't actually the case for the examples I cited or hundreds of others. There are two kinds of bankruptcy, the SHLD kind that is obvious for some time and the unexpected kind due to some kind of external shock to the financial system (i.e. Bear Stearns) or fraud in the financial statements. I'm not in any way suggesting that I suspect IB is engaged in financial statement fraud or that we have a systemic financial shock imminent. However I am quite adamantly insisting that by their very nature both are unknowable until after it's too late to do anything about it. To think otherwise is to ignore history, much of it very recent.