my desktop is connected to ADSL via the telephone socket & cable
Hmmm - telephone socket on a desktop? Could be an RJ45 ethernet port.
Famouswhendead - please tell us what your desktop PC and laptop make and models are.
Also, please tell us what the cable is that connects your PC to the ADSL modem - look at the plug at the end of the cable and see if it is like this:
If it is, then you are connecting via RJ45 ethernet. Is there a similar socket on your laptop?
SD