Hi, well problem solved but without really getting to the root cause. I did a factory reset and then re-entered all of the original settings as per my original post and lo and behold the router achieves dsl sync and establishes a PPPoA connection. IP address is assigned and internet access is possible. The message 'Dial PPPoA Connection' in the WAN status field is now replaced by 'Drop PPPoA connection'.

Connection has been stable now for several days.

So, perhaps some corruption somewhere in my settings initially despite them appearing to be OK.

Thanks for your interest