Many thanks for responding.
The previous modem (a thomson) was consitently 3-4 meg and sometimes more.
The speed download test came back with 0.22MBPs. The response is poor, i.e you cannot stream a You Tube vid withoit it pausing every 5 seconds. This was not a problem previously. The ISP service hasn't changed, the only change is the N600 and a new wireless LAN.