This is, sadly, my experience, too, except when at work where I get a passable speed. I forget mostly because at home the wi-fi takes the strain (well as much as crapp old Plusnet can or will) but on holiday the week before last it became apparent.
We struggled to get decent internet and in the absence or wi-fi and aided by the slow speed burned through a goodybag and had to bring one on early to avoid losing all internet. It has always been slow for me but I have got used to it to some degree. If it doesn't improve and also phone coverage I guess I would look around to see what other optiosn there are now but I would rather GG stepped up and I'm not going down the contract route again.
I guess I may end up down the supermarket PAYG route eventually.