At least in Germany we had the so called "Routerzwang". Some ISPs allowed third party equipment, but many didn't. You'd get a modem / router / AP combo device and the ISP had complete control over the firmware. Since there was no competition, most ISPs didn't care about the quality of their software or even security updates.
Thankfully in the UK all the (cheap) ADSL suppliers I've used have provided a modem+router+AP in which you can just read the access credentials off the config screen. No need to spoof MAC or anything when setting up a new 'router' just use the right credentials.
Now I'm wondering why, whether it's legislation or the way our ISPs relate to the infrastructure.
Primarily because our phoneline also comes from the same ISP which has to use their shitbox. They don't give you the credentials for that, you get a pretty configured router. It's possible to root the box, steal all necessary credentials and clone the mac but that is a huge hassle and obviously not supported.
I had similar issues, and I complained enough that my ISP gave me a second, just plain stupid modem and a splitter, so now I have their fancy phone/modem/router/wifi one just for the phone, and a simple modem only box for my actual internet. Works like a charm now!
Interesting. I am moving soon so I have given up the fight for now, but I might have to aim for that after the move. Thanks for the tip.
Just keep in mind, their "first tier" of customer support probably can't authorize that kind of thing, and probably won't even know what the heck you are wanting. I complained about the crappy slow internet and bad ping until I got to their actual tech guys, and told him the older modem did better, and he was like "Well, why don't you use one of them?", I said "Need the phone", and he told me to just put a splitter on it and use both, he'd set it all up and have the local office put one aside for me. I only even pay rent on the one modem, so it's actually an amazingly good setup, other then meaning I've got the start of my own "commercial grade" networking setup attached to a wall in the basement, with the modems, the router, a switch, and a server.