Since we have had the broadband connected into the test socket it has disconnected again and the noise level is even worse (15dB). So the problemn is no within the wiring in the house.
I have since found out that our neighnours were having issues for the past month (about the same time our issues started) and a BT engineer has been working on the pole where all the phone lines are connected and also some underground connections were flooded further down the road.
So we either have the same problem as our neightbour or the work they carried out disturbed something on our line.
Because of this we have phoned BT directly and they are monitoring the line and said if nothing improves over the next 24 hours contact them, they will send out an engineer as it sounds like there could be a problem with the line.