BT it sounds like are advertising the 150Mbps product with the line average speeds of 145Mbps.
TalkTalk are advertising ALL of their fibre products saying "average speeds up to 145Mb/s". When following the link it then shows you 3 products and the top product states average speeds of 145Mb/s. Technically I believe the advert is correct.
You should be able to see it from this
google. However, I haven't see the specific advert itself.