Flashing on the front is legal these days (the law changed around 6-8 years ago IIRC). I tend to use a Cateye EL135 blinking around dusk to attract attention.
I think you're right, flashing lights are legal, front or rear: http://www.ctc.org.uk/cyclists-library/ ... egulations
I have a Blackburn Mars 3 on the rear: http://www.bikeradar.com/gear/category/ ... ight-29565
. I always have it set on flashing and it's pretty bright.
On the front, I have a Cateye Nano Shot Plus: http://road.cc/content/review/72875-cat ... ront-light
. Quite expensive, but it gives out plenty of light for completely unlit roads and the "hyperconstant" mode where it pulses between the high and low settings is very attention grabbing, and because it's never completely off you can still see the road and the numerous potholes well enough without having to change to one of the continuous modes.
I also have enough retro-reflective stuff on my regular night riding bike to ensure that even the most myopic motorists have little excuse to use the "sorry I didn't see you" phrase.