Generally, if you change broadband provider your new supplier will install their own terminal box into your house, whilst leaving the BT box in situ, as by law there must be a BT connection to your house. However, there's nothing to stop you having multiple providers, but your new providers cannot use the exising landline connection to your house, i.e NOT BT connection.
I had this problem with my broadband a while ago and contacted my provider. They checked the line and found that there was a problem with the BT line which caused the slow connection. It might be worth your while contacting whoever you get your broadband from and see if they could run checks for you. You do not say who you are with at present (I am with Plus Net and would recommend them highly for customer service) as I know that some companies have very poor customer service and are hard to contact.
TalkTalk has a 50 to 1 contention ratio, which means that you could be sharing your connection to the internet with up to 50 other users.
That's fairly common for 'budget' ISPs. You could probably get a better connection speed if you switched to a decent ISP but it will almost certainly cost you more. (My ISP has a 7 to 1 ratio, but I pay 'business prices' for the privilege).
Even so, it's not uncommon for people to find that their connection speeds have dropped over the past year or two. That's because more and more people are using data-heavy services such as the BBC iPlayer.
It's also worth remembering that one person's definition of a 'poor' speed might be different to someone else's. I'm a two-minute walk from the exchange but our area hasn't yet been converted to fibre-optic cables. So 5.8Mbps (which I'm currently getting) seems good to me. It's 5 times what some urban areas get but it's still slow by the standards of certain parts of the country.
Chris, Talktalk always seem to get a lot of flak. I have always found them great for customer service and anything else. My current broadband speed is around 12mps which is plenty fast enough for me. For £10 pm they can upgrade you to fibre optic broadband which can double the speed but I do not need it. Hopkirk, you dont say if you have contacted the ISP. What is your speed? Talktalk website has a speed checker. There are things you can do to make it faster. Clearing your browsing history is one.
It is sometimes possible that the modem is giving trouble. I used to think that a modem either goes or not, no inbetween.
I had a lot of trouble with my speed slowing down to less than dialup after a few minutes, often having pages time out. After many calls to my ISP they suggested another modem so I connected an unused Thompson modem and all my troubles were gone. Tried the old Belkin again, and again the trouble started again so it must be the modem.
We are also with Tiscali/TalkTalk and will definitely leave when the contract is up. It's pot luck if you get a helpful adviser on the end of the phone. We have had so many problems with poor BB speed, even as low as 0.1 Mb at times. On their advice we now get about 1MB but that's by having the wire straight into the BT socket, bypassing the phone and the fascia hanging off. TT say beyond that any problem is BT's.