Follow the link on this post and either sort by price (this is ex VAT before discount) or sort by model name to find the Mini 9 series.
Example Spec (There were 5 of these at time of post)
Operating System: Operating System Ubuntu Edition Version 8.04
Memory: Memory 512MB (1*512) 533MHz DDR2 Dual Channel
Hard Disk Drive: Hard Drive 4GB Solid State
NoteBook Screen: Display 8.9in Widescreen WSVGA with TrueLife
System Color: LCD Back Cover Sticker 1 Black with WLAN
MISC: Keyboard Internal UK/Irish Qwerty Keyboard
N-Series Inspiron Mini 9 Diagnostics and Drivers
Battery Primary 4-cell 32W/HR
Dell 802.11b/g Wireless LAN Mini Card
Discount Voucher Offer Valid on Stock in Dell Outlet
To avail of this offer all you need to do is select your desired system, add it to your shopping cart, then tick the "SAVE £55" offer in the Software and Peripherals Section once you have added your system to the shopping cart ! It's that simple!
Offer Ends Midnight Thursday 30th April 2009.