Nope - but the voltage on the line is between 50 and 60 volts (depending on the exchange) so you could get a bit of a shock. And if you short the wires on the line side, you could get a visit from an angry engineer, and a bill for any damage you cause. Also, the phone company owns the line up to the master socket, so if you are cutting on the line side of the master socket, it could be construed as criminal damage.
what!that's crazy, they are in my house, surely i can't get done for that? and how would they know that i've done it as i don't have a phone, tv or cabled internet
If they are connected at the exchange end, they'll no you've done it because by cutting the cable you will remove the terminating resistor, which will show as a line fault.
Why do you want to cut it?
I was in this position some years ago when an additional phone line was connected to the upstairs. When it was no longer needed I simply removed the wires from the internal junction box - problem solved. The only down side to this was not telling the phone company that the line was no longer required and the previous line user kept getting charged for the line rental. This of course stopped when I told them. Just out of interest, there will be no screws to loosen inside the box, just a number of thin wires easy to remove. If you have no use for it tell them and save line rental.
The previous owner had them installed and i assume that after he passed away his family had the phone and internet cut off but left the cables there. He also had sky tv and they or the company physically cut the cables for this themselves before i moved in. i had the wall they were attached to knocked down and now i'm left with just a couple of boxes and a long line of wires that are just getting in the way. maybe i should just call the company and see what they say
With this being from a former occupant, you will not be paying line rental but there is nothing to stop you taking action as outlined at 23.57 17.11. If you don't feel like opening the junction box, just give them a tug and they will remove easily.