I know this is probably not the cause, and maybe it's just me being a naive SJW, but in my view London's financial institutions lost 90% of their credibility capital recently not so much because of Brexit (which hit them too) but because of the whole LME Nickel trade rollbacks shenanigans. Yes I know LME != LSE, and I know it was a lose-lose situation, but they co-exist and as a person who is not into finance they share their credibility to an extent.