I am an ex-BT Engineer and the distance from the Exchange can make a huge difference. Its all about loop-resistance.
You have a pair of wires, all to yourself, that runs from the Exchange to the junction box in your house. If this is a long distance, then the loop-resistance will be high and the losses involved in the signal will also be higher. Telephone conversations aren't much effected by high resistance, in normal use anyway, but internet connections are.
Most of BT's networks was installed in the 60's and 70's, using copper for the cables. But when copper became expensive in the mid to late 70's, BT changed over to using aluminium for the conductors in its cable, to save money. Aluminium isn't as good a conductor of electricity as copper, so losses were increased.
Not really a problem for telephonic use. But now that our telephone cables are used extensively for the internet rather than telephones, it can be a problem if you live a long way from the exchange.
BT are improving their networks by a program called Copper Offload. This involves replacing the copper and aluminium conductors with fibre optic cable. This may be all the way to the "cabinet" ( green box thing ) beside the road nearest to your house. Most people will still be left with a copper or aluminium "tail" into the house but speeds should be dramatically improved.
Some new housing developments are being provided with fibre optic all the way. Companies like Virgin are putting in rival fibre optic networks, independent of BT.
But remember to bear in mind that most of us get our internet signal from our telephone line and almost everybody still uses the BT network. This after all was put in when BT was still called the GPO ! It will be some time before BT gets around to replacing the metal with fibre optic to everybody in Britain. If you live in a rural location, it may be a long time before things improve.
All this may be nothing new to a lot of AB'ers but hopefully its helped some people.