It's up in the Shop now:
http://www.underworldlive.com/shop/digital-audio
£1.50 for MP3, £2.50 for WAV.
Also available together or as individual tracks on UK iTunes, UK 7digital, UK Beatport, and trackitdown.net, although if you're buying more than 1 track, it's probably cheaper to buy it from uwlive. (trackitdown.net seems to be the only one you can use in the USA.)