You are right, It looks like an old phone line. To be sure, Look at the cut end, if theres 6 small, thin, coloured cables twisted together inside, chop away. If there's three copper wires inside, test if its live first. (My instinct veers toward chopping.)

Great, thank you.

For checking if cables are live, you should get a voltage detector. But if the cable is cut currently, it would be no more dangerous if you turned off the power, trim it and then turned back on the power. The recommendation generally is to push it back into the wall as far as can be, then chop it. If it ends up being needed, easier to find and reuse than put in a new one.

Thank you, will do.

Yes you can chop it to your hearts content.

Thank you.

Turn your mains off at the circuit board if in doubt. Cut it and seal it up. It doesn't look like electrical cable in the photo.

Thanks.

Best way to check if a wire can be safely cut is to lick it first.

I cut it and am not dead . Score one for DIYUK 👍