if it is the case as you say that DHC{P option 61 is not required, then why on other forums are people saying they can't use their own router on Sky ?
you said DHCP Option 61 isn't required on all Sky/Now, notice the ALL, so it may still be required on some.
I went in to that in detail above.
The majority of Sky/Now connections can use DHCPv6-PD to authenticate, which most routers support.
There is a small percentage (that's falling) of Sky lines that need DHCP Option 61 because their DHCPV6-PD implementation doesn't work through some Openreach kit.
It's not as black and white as my router doesn't have Option 61 so I can't switch to Sky. It will likely work with DHCPV6-PD and failing that there's a chance Option 61 can be added to the router.
There are quite a few routers out there that don't support DHCP Option 61 out of the box with the default firmware but it is possible to enable with config changes or 3rd party firmware.
Every single Asus device for example has no Option 61 in the stock firmware but it can be enabled with the popular Merlin firmware.
There are many more router brands that can have open-wrt or dd-wrt installed and both of those support DHCP Option 61.
It can be done on many Zyxels by editing the config file with the Option 61 hex values.
Not every user has your circumstances and not all responses are aimed at your situation.
I was simply trying to be helpful for anyone who may read this thread in the future.
It was assumed for years that DHCP Option 61 was required which is why you keep reading that on other forums.
I'm not aware of any other UK provider who authenticate like Sky and can give the IPV4 WAN address over IPV6 (via DHCPV6-PD) which is probably why nobody ever tried it until a Sky rep posted it on their forums a few years ago.