Comment by pumplekin

This is due to advertising standards. They are required to advertise "average speed", although how this is actually calculated is nebulous.

A&A not advertising can just say what the link speeds actually are on the product pages.

Other ISP's could do this too, but it would cause confusion having one figure on the advert and one figure on the product pages, and they might get in trouble if they link to the product pages in the adverts.