open up a VPN on your computer, (I couldn't do this on the starlink app, prices continued to be in £££). Go to starlink website, register the kit and select the service you want. it was as simple as that. I used wise (like revolut) to pay in Euros although im not sure if that mattered or not. I picked an address of a supermarket in France as my address and entered that.
I have no idea if this is going to continue to work or not. Or if they'll tell me to move it to a UK address after 2 months? I don't know. But I did pay for roaming, and it works fine in UK after signing up with a French address. One of the people on the discord told me he's done the same and the speed is the same as his UK registered one.
I'm taking the risk doing it and finding out, I don't know how long it will last for. But it's working great and it's almost £35 cheaper than paying for UK price + roaming. I should say that I got kit from currys not from starlink. If you get it from starlink, it will already be registered for you, at your UK address / the address you had it posted to.
One other word of warning, once you set your address to France or elsewhere, you will NOT be able to order accessories like the ethernet adapter etc from the starlink website. It will only allow them to be shipped to the address you chose to sign up using. So in my case, I can only ship accessories to France. I just had to pay £9 extra to get the ethernet adapter from Amazon instead.