The post-production market in the UK seems to use PTHD with Windows, for some reason.
be that as it may, based on my knowledge and research of UK music tracking and mixing rooms, the overwhelming majority are outfitted with
Macs running PT HD.
for instance the Miloco studios, such as...
The Engine Room
The Engine Room Protools Specifications
Top of the range protools system based around an HD3 Accel system. Either protools or logic pro software can be used.
Hardware
Apple MacPro 2x2.8 Quad-Core, 4GB RAM, Apple 23" Cinema HD Display
1 Triple Glyph GT103 removable firewire chassis
Choice of removable hotswappable firewire drives 160 gigabytes each
3 x Digidesign 192 interfaces providing 24 inputs & 48 outputs
Digidesign MIDI I/O interface
Digidesign Sync I/O synchroniser
Alpha Centauri
DAW Hardware:
Apple MacPro 2x2.8 Quad-Core, 8GB RAM, NVidea 8800 GT 512MB, 300GB HD, 2x 500GB HD, 1x 1TB HD, AirPort, 30" display
PC Dual Dual Opteron Win XP SP2 running Cubase 4, 32 outputs (Apogee AD16-X), 16 inputs (Apogee DA16-X)
Sonifex RB-UL1 Unbalanced to Balanced Single Converter
Digidesign ProTools HD3 PCIe
Digidesign MIDI I/O
Digidesign Sync HD
and
Assault & Battery 2
DAW Hardware:
Apple MacPro 2 x 2.8ghz Quad-Core, 4GB RAM, 300GB HD, 2x 500GB HD, AirPort, 30" Apple display
Digidesign ProTools HD4 PCIe
Digidesign MIDI I/O
Digidesign Sync HD
and the infamous
The Chapel Studios
192 Tracks of Pro Tools HD3
4 x 192 interfaces with expansion cards in each
AppleMac G5 2.5GHz dual
the much touted
Strongroom
Apple G5 Dual 2 GHz
Pro Tools HD4 Accel
the list goes on and on....