Speaking from a slightly informed viewpoint ...
The business is not deserting London to Frankfurt or Paris, much as they would like. What is currently happening with Covid though is there is extensive on-line Teams/Webex working around the offices and with clients, much of this from people's dining tables (including the other side of mine
). It has also been the case that Canary Wharf finance offices have employed a high proportion of EU staff from all over, a good number of whom have currently gone back home and are working, again from their dining tables, in Athens or Lisbon etc. These are still UK company workers, and many are quite keen to get back to the office at some stage soon.
UK senior staff, along with New York and Singapore, have much of the worldwide knowledge and are not attracted, and even more not their families, to Paris or Frankfurt. Those examples of staff I gave from Athens and Lisbon are likewise not attracted there because, unlike their English, they are not fluent in French or German, and the general feeling is that you get marginalised very quickly. It's exactly the same as UK staff who ended up at Airbus in Toulouse felt.