I've just read article in Techworld newsletter headed:-
DDoS fear as 24 million home routers fuel hidden DNS amplification attacks
I don't claim to understand it but a feather in tbb's hat for being the link at the end of the article for testing their settings
"Most home users will not find their routers behaving as DNS proxies but anyone that wants to check can test their device.( link to ttb)
My router is one of them so now I will have to try to understand how to correct my settings.