Simon
Keefers link shows the clutch needing held to loosen/tighten the alternator nut.
I found the vise grip type clutch holding tool that they used in the Haynes manual is made in the states with a UK Distributor Motion Pro part number 08-0008
Heres the website
http://www.motionpro.com/Docs/servicetools_3.html And this lot sell them in the UK, around £ 22.00 inc postage, it works well and the company below delivered next day
Allen's Performance R&D
Unit B9, Moorbridge Road
Bingham, Nottingham NG13-8GG
Phone: 011-44-1949-836-733
Fax: 011-44-1949-836-734