Meridian specify a minimum standard of Cat 5/6 STP.

Having BTDT with this, my experience is it does make a difference between shielded cables, but nothing huge.

In the end, I've come back to Meridian's own 'flat' Speakerlink as the best all round sounding cable for this application. I know they did listening tests of a bunch of cables at the time and chose that for its sound quality as well as technical merits.

Speakerlink Datasheet
Photos, etc.

It also has the benefit of being very flexible and easy to hide.

I do wish they would make a 2.5 or 3 metre length, though, as the gap between 1m and 5m is probably where the most common length needed for SL -> Speaker runs lie in the average British lounge.

HC: 861v4/ID40/LPS, DSP5000, DSP5000VC, DSP3100, SW1600, HD621, Oppo BDP-105, Sony VPL-HW55ES
2-Channel: Oppo BDP-105, TEAC VRDS-7/Trichord Clock 3/PSU, 551, Quad 303, Harbeth Compact 7ES-3, Kimber cables, Russ Andrews mains and supports.
Previous Meridian: 5000C, 5200SL, 7200.2, 6000, 562V.2, 568.2mm, 800v4, 808.2i, 818v2/v3, 861v8, 502