But as usual the truth is a little harder to reach. A large proportion of these transactions are undertaken by a kind of subsidiary of the LSE in Amsterdam so in fact the number of transactions orchestrated in London has increased.
Yes, there is an LSE subsidiary in Amsterdam, but it does by no means make up the pending loss in any way.
The reality is that Britain's access to EU markets is limited for the time being. At the beginning of 2021, a lot of the EU-related trading moved -- and not only to Amsterdam, but also to Paris, Frankfort, Singapore, New York, HongKong etc etc -- albeit, and hopefully, only temporarily. In fact, right now, even Burmuda has more access to EU markets than the UK, it claimed somewhere.
Why? Because the Brexit deal has absolutely nothing to say about the financial service sectors. Negotiations concerning a UK/EU deal for UK financial services are continuing (until end of March, probably longer). At the very heart of it is 'equivalence'. This means, from a European point of view, whether the UK will continue to use the MiFID II regulatory framework or not (i.e., post-Lehmann-shock regulations concerning investor protection, transparency etc etc etc). If the UK doesn't, the EU is very likely to cut London off, as they fear that Britain might otherwise try to undermine EU markets (alternative trading platforms, europound). But even if the UK does, the EU still has a strong interest in further advancing their own financial service sectors.
Either way, expecting a no-deal scenario, assets of over a trillion euros had been transferred from the UK into the EU. It's too early to tell, but in pre-Brexit times, the UK financial service sector contributed 6% to GDP and almost 10% of state tax revenue (these numbers need factchecking).
But as always, I'm optimistic they will sort it out. Maybe not Johnson himself, cos he has to answer to the North of England where he won the election. Anyway, there's also talk that London might reinvent itself yet again (similar to 1986) -- this time as a hub for green investments, fintech, cryptos and worldwide FX trading.