Just popped into John Lewis, Oxford Street they had this deal via a leaflet near the Kenwood kMix mixer, Its only through participating Stores.
The deal is valid for purchases made between 19/10/09 and 24/12/09 although £299.99 for the mixer is not the cheapest out there, if you are interested in buying both I think this would be the cheapest combo price you could get and it may come down prior to Christmas or you may find a reduced one etc (it says not available with other Kenwood promotions so I assume reduced machines in JL is acceptable)
The blender is actually quite nice, and although not as nice as the KitchenAid range looks good and hopefully does just as good a job.
p.s. you have to send off a form for the blender you get it sent in the colour of the food mixer you buy and it takes up to 28 days to arrive.
for reference this deal is also available at a few other places found via google:http://www.google.co.uk/search?hl=en&client=firefox-a&channel=s&rls=org.mozilla:en-GB:official&hs=Myo&q=FREE+KMIX+BLENDER&start=10&sa=N