My parents had a similar issue recently, connection speed was around 0.43mb but they did have noise on the phone line.
Tried unplugging all house phones and plugging router directly into test socket with new filter, no difference.
Got them to call BT to sort the noise on the line out,which seemed to be a fault with some old external wiring as the line has to pass across 2 adjoining properties.
Then got on to Sky who checked there guff and reset the DLM, also got them to send a new router out.
I also fitted them a new faceplate to the master phone socket with integral filter.
Result connection speed is now upto 4mbs with hopefully a little more to come once the DLM is done, which is fine for them.