My Son has just got me a 0.5 WATT rear light for £4.99p made by Oxford. The rear light is also the same as 'Smart Lunar' which sells for £13.
The shop TK MAX in Mansfield has a big stash of them so I'm assuming other TK MAX shops have them in too, but not for long at just a fiver.
Batteries/bracket/seat post/seat stay adapters included.
Not the normal cheap crap you see and they are very bright.
They are the same as this one
http://www.ebay.co.uk/itm/Bike-tail-Lig ... 4abbe13c3a
I hate RED DWARF