Here's a little tip I used that increased my download speed. Much telecom wiring is similar nowadays, so this may work in the UK.
When I first moved here I was getting 2.5mbps max and France Telecom reckoned that was not bad for here. After complaining a number of times they sent a broadband specialist who after testing the external wiring asked if there were extensions throughout the house to plug other phones into. There were three other extensions in various rooms that were unused because we had a cordless phone set fed off one socket. He was not allowed to touch any wiring inside the house but suggested I disconnect the unused extensions at the distribution box, leaving only one in operation. It was fairly simple to do and immediately the speed went up to 5.5mbps. I don't know how that worked, but it did.
Another tip he gave me was to do a "hot" reset of my Livebox (router) by unplugging the dc socket from the rear, wait twenty seconds, then plug it back in to reboot. Speed tests before and after this procedure showed it also worked.