"Andy" wrote ...
I am in the UK.

I would like to take a stereo signal from the line-out of my stereo
(or TV) to the line-in of my PC.

The equipment is in different rooms and the audio cable would be 10
metres. It will be this type:
http://www.maplin.co.uk/images/full/130i0.jpg

I don't understand the technical side but is 10 metres so long that
it might cause audio problems with things like frequency response or
voltage/current levels and so on?

Will I need to get some higher specification audio cable to cover
that distance? I want to keep cost down.

The cable is most likely just fine. However beware of
ground loops and other hazards of running audio over
long distances. These have little to do with the cable.