Parker's are selling Castrol Magnatec at half price in and around the East Midlands. NOT AVAILABLE ONLINE.
Corby, Retford, Newark, Nottingham, Melton Mowbray, Grantham, Leicester : Abbey Lane, Knighton, Syston, & Thurmaston Loughborough http://www.thepartspeople.co.uk/branch-locations.html
£13.49* including VAT. *Petrol engines. Max 4 per customer. Expires 30/11/08
5W and 15W also at half price. And for diesel engines too.
Click link - Halfords for product details.