We decided to give in and give up! The ISP-supplied router wouldn't respond locally or remotely so I've - for the present - reverted to my previous router, which I just got working adequately after realising that the colour-coded purple cable to the internal router wasn't the colour-coded purple cable it should have been but a different shade (and where it is is a bit dark)
Still haven't sorted out the original issue over IPv6 though!
#CallThisLiving? #tech #geek