Double galzing.. the down sides

Hi

Im from the Uk and hoping someone can prove all the answers without me trawling the web!

My house is 10 years old has wooden double glazing and is painted in the most eco friendly paint i can find at the time,

Just been visited by double glazing sales person who wouldn't take no for an answer but would like some more smarter replies to give hem next time , their sales pitch is that government looking to tax houses that are not energy efficient more than those that have the latest technology. Started his sale pitch with see you have wooden windows, how much better PVC was, responded PVC not environmental friendly windows in good condition no need to replace..I'm not interested, then went on its not the frames its the glass, yes well while mine not be pilkington special K the best glass at the moment they are functional and i see no reason to replace them... but want some smart replies to their sales chat

any takers