Excellent. I wondered if i had a weird model or something.
@Jamauk - Thanks a lot for your post. It gives me something to work from so to clarify the steps would be
1 - Reset everything to defaults to fix anything i've messed up so far!
2 - Re-Configure the Raspberry Pi and install the controller software. Set a static IP - Say 192.168.1.5
3 - Connect HG612 to USG
4 - Connect USG to my laptop - Go to 192.168.1.1 and set up the PPPoE. I presume i can test this works by my laptop being able to see an internet connection
5 - Unplug the USG from my laptop and plug it into the switch.
6 - Plug the Raspberry pi and Access points into the switch
7 - Using the laptop log into the raspberry pi unifi controller using 192.168.1.5:8443
8 - Go through settings on the controller to adopt the 3 Unifi devices (USG and 2x AP's)
9 - Cross fingers and pray everything works?
I think part of why i struggled last night was that i couldn't seem to get access to the RPi when connected to the switch. Does the USG still do a job of setting up a network/routing devices before it's adopted and setup?
I presume doing all the above would mean that there is no IP address for the HG612 modem and therefore no way to access the inbuilt GUI?