If you have a Webstar modem, the white coloured one with the wavy side and your ex-Telewest, then your modem is off frequency.
192.168.100.1/gscan.htm
Delete the starting frequency type in 331000000 press enter, you should get a message saying set successful and the modem will reboot. Check levels again on Signal tab, if still showing 33075 you need a replacement modem.
If ex-ntl ignore my post