In reply to TMM: Plenty of good back and front packages available from Wiggle, Planet X, Evans and the like. Rear LEDs are so cheap these days you can get a couple to fit on different places - like on the trailer perhaps.
If you can wait a few weeks to get it, looking at the stuff on Deal Extreme from Hong Kong is worth it. I've just ordered a second one of these:
http://dx.com/p/trustfire-tr-801-cree-q5-wc-230-lumen-led-flashlight-1-1865... it is ferociously bright yet small and and easily popped in a bag when not needed. You need to buy the batteries and charger that go with it, but that's just a few more quid, and a bracket like
http://dx.com/p/universal-adjustable-bicycle-mount-for-flashlights-2cm-4cm-... I'm buying a second for off road mountain biking in the dark. The one is absolutely fine for seeing and being seen on the road.