Are these old telephone wire?

[Reginaldperrin]

If so are they safe to cut? They lead outside windows. Thank you!

Yes. You can cut them, it's not dangerous - but anything connected to them will stop working (like a landline or broadband router).

Thank you @pinkgown

Who's your internet provider? Provider's like BT, or any provider using BT's system still use those types of lines for internet and phonelines.
If you cut the master line, then it may affect these services into your home.

I wouldn't cut the one that has the BT logo, as it is likely to be the master socket. (Unless you have a new one elsewhere.)

Just be careful. I once cut an old telephone cable only to find that it was the wiring for our house alarm. If you have an old alram.....just check its nothing to do with that

In the second picture, there are two BT master sockets. The smaller, yellowing one with the old "T in a circle" logo has likely been replaced at some stage by the newer/larger/whiter one next to it.

Technically these sockets belong to Openreach who inherited the telephone network infrastructure from BT. They will have no interest in the old one on the left, assuming it is no longer connected, but the right-hand one may well be live (or at least connected to the phone network).

Even if you actually use e.g. a Virgin Media cable for your broadband, the current telephone master socket should remain in place in case you want to shop around for broadband later. If you want the master socket to be moved to a new location you are supposed to ask Openreach to do it, not DIY.

Super helpful! Thank you all.