thanks works now, yeah isnt well designed.
It might feel awkward but actually seems logical to me.
The first step is to enter a postcode. If you don’t know that you are wasting your time, and wasting the server’s time, so it is right to make it clear that it is a fundamental requirement, without which you are doomed.
You then want to select a pulldown address from the postcode, but doing so unimpeded might impose an overhead on the server. It might also attract bots that just want to build lists of UK addresses for junk mail, so that is the correct point in the sequence to insert the captcha - after postcode, but before the pulldown list.
Together with the correct technical terms FTTC/FTTP rather than nonsensical “super-fast” or “full fibre”, I get a warm feeling that this thing was designed by engineers.