International investment banks could have as little as a year to overhaul their European Union branches and shift sufficient staffing and other operations to the EU as the bloc's regulator ramps up activity to crush post-Brexit non-compliance.

The European Central Bank has been pushing banks to bulk up on the continent since the Brexit vote, shutting down loopholes to ensure that lenders shift more staff and key functions to the continent as part of its so-called desk-mapping review.