Worked for me.
Took literally 20 seconds and I had an IP and everything burst into life.
Are you on G.Fast WM?
No there is absolutely zero requirement to extract username and password from the device. The only requirement is for option 61.
Generally sky agents beyond a certain level, if you reach them, will recommend
Generic Username And Password
This will work any custom router that supports DHCP option 61 (MER).