As far as Brexit headaches go, Barclays' John McFarlane says that while his bank is on top of job relocations, he's more concerned about rewriting “hundreds of thousands” of contracts.

He's not alone. Andrew Bailey, head of the U.K. Financial Conduct Authority, said “contract continuity” is among the biggest potential disruptions in a no-deal, no-transition Brexit. Both Bailey and McFarlane, who also chairs London's banking lobby, testified before lawmakers Wednesday. Bank of England Governor Mark Carney and European Central Bank President Mario Draghi have also expressed concern about the issue and the lack of time left for a fix.

A week ago, data from the European Banking Authority showed the scope of the issue, and that money is already on the move for that reason. European banks have slashed their U.K. assets by $425 billion, driven by a 35% drop in derivatives exposures. Insurance policies are affected too, with Carney saying that about 20 billion pounds ($26.9 billion) of insurance liabilities in Britain could be affected without swift action.