As I understand it the Broadband providers all have their own equipment in the exchange and I think openreach only do connections and cables. If I change provider I assume they will be swapping over equipment and therefore I might solve the problem. Is that what you found Shayne ?
Not all. Some do. Like talk talk and sky( again only in some places, its called llu where an ISO has their own equipment in the exchange and lease lines to and from the exchange from BT ).
The whole setup is mad complex with different products and contention rates and over commit ratings etc. Essentially going with a BT owned brand in places with bad connectivity like PlusNet can help make it easier. On the other hand is like Zen as well as Andrews&Arnolds are far more clued up and will help on the technical side with custom profiles for specific lines etc.
What you really want is to get your modem as close to, if not into, the master socket to the house. This can also make a huge difference. Then ask the ISP to tune the profile for stability rather than speed. You might get slower but it should stick a lot more with fewer line drops. Then another thing to check is use a good ADSL splitter. Some of the cheap £1 ones can themselves be causing static issues. Finally, you can likely setup a retrain profile on the modem itself. Depends on which one you have, and how much admin it lets you do.
This is literally just the tip of the iceberg, but a few things to start with.
You might also want to check with Sam knows about the real status of your exchange and cabinet you connect to. Sometimes, rare but I know 2 people who lucked out, if you are in a dense area there might be an option to get a line from a different cabinet. Typically inner London like density.
Finally make sure your modem isn't hacked or at risk. When you think the net is slow, you might just be actually participating in a bot net flood attack somewhere, and that is eating up all your internet speeds.