It seems a bit of a mistake, but John Lewis are advertising on the website a Mac Mini 1.83 GHz Superdrive Desktop computer for £399 the RRP is £529
To add to the confusion the description seems to be partly for the new 1.66 ghz duo (combo drive and 60gb hdd. The model is MA607B/A which is the 1.66ghz combo desktop). However the processor is listed as the 1.83 ghz chip and the headline title is the superdrive model.
It might be worth a try to see what you get. The online order can be further discounted by using the £15 off orders over £75.