Running telephone extension next to power cabling

I have a telephone extension (installed before me) run from the master socket surface mount round a number of doors ways, through walls etc and it looks unsightly so as I'm decorating some of the rooms it passes through I thought I'd sort it out.
I have a couple of options on where to install the extension socket but the route the cable would take is quite similar for both. The easiest route to get a cable into the wall (Wall A) would actually mean running it down into the wall alongside existing ring main wiring, (pull ring main up, attach cable, pull down again) but I'm aware data cabling next to power is a bad thing. I then found another possible location (Wall B) where the cable could come down the wall away from power cabling.
However, working back towards the master socket under other boards, I've found that another extension and I think even the master socket cabling both run through joists alongside ring main power cables - this would have been done when property was first built ~20 years ago. So I'm wondering how important it is to keep the telephone extension away from power (now knowing it's already done been in a few places)? Can't find much in the way of shielded telecoms wiring online to minimise potential EMI. Anyone had any experience of this?

Thanks

Running twisted pair telephone cable ( CW1308 standard ) next to domestic mains power cables will not induce any noticable hum on the telephone line.

Flat telephone cable where the wires are not twisted will pick up hum as will some of the cheap stuff that has too few twists per meter and / or uses poor quality metal instead of copper..

Thanks for your reply @bernardgreen. When you say noticable hum, I assume you mean audible hum? Rather than describing interference on the signal as hum. I'm planning to plug a phone and router into the extension socket, not sure if that makes any difference. It's the internet connection I'm most concerned about (should have put that in my original post sorry).

fixo said:

It's the internet connection I'm most concerned about

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Unless there is a lot of high frequency noise of on the mains cables the effect on ADSL ( broadband ) signals will be insignificant. The occasional data package may be disrupted if something is switched on or off but error checking will detect it and auto correctit without you realising it happened.

Sources of high frequency noise on the mains are switch mode power supply units, ( often refered to as "electronic transformers ), dimmers, units that send data over the mains wiring ( PowerLine ) and other electronic devices.

bernardgreen said:

Sources of high frequency noise on the mains are switch mode power supply units, ( often refered to as "electronic transformers ), dimmers, units that send data over the mains wiring ( PowerLine ) and other electronic devices.

Click to expand...

Ah ok, the power cabling that the extension could run parallel with terminates at a double power socket that I was hoping to use to power the router + phone and a powerline adaptor to get the router as part of a wired network. That might be an issue then I guess..

I've been doing some reading (primarily here) and am now thinking of using Cat5e for the telephone extension (something like this). I've tried to avoid power routes but there are a couple of places where the telephone extension will have to run parallel with mains power. I suppose there is no point in trying to mitigate interference by getting any shielded twisted pair (f/utp or u/ftp) as I think I'm right in saying there's nowhere to connect the shield/drain wire in either the master or extension telephone socket?