An update!! (After lots of time on the phone.....!)
I believe the power supply to be good as I have tried another aftermarket one (rated exactly the same output)..... However, NTL have insisted on shipping out another power supply and won't ship out a modem until the psu has been replaced...! I am waiting patiently for delivery tommorow, then I'll call back and say it still won't work!!!
Cheers,
Baz