Hi Andrew,
As you mentioned the deadline to request a move to the UK data centre has passed. You have a couple of choices going forward AFAIK. I’m willing to be corrected!
You could choose to provision a new tenant which will give you the ability to provision to the UK data centre from the outset.
This may not be practical so consider if you need to move at all. Many UK organisations continue to be based in the European data centres with no impact.
One final choice if you have jurisdiction concerns is to speak with Microsoft UK directly to see if they can help.
There’s lots to think about including the size and complexity of your current Office 365 deployment.
Hope I’ve given you a few options to consider!