relevant bit of the highway code
Flashing lights are permitted by you are also meant to have pedal, front and rear reflectors and lights that conform to a BS standard.
The also a thread recently about allowed power of lights.
Interesting reading those "Rules" as many are actually recommendations, things which they state you "Should have or do while actual rules are are stated as "Must" where compliance is mandatory...
At night your cycle MUST have white front and red rear lights lit. It MUST also be fitted with a red rear reflector (and amber pedal reflectors, if manufactured after 1/10/85). White front reflectors and spoke reflectors will also help you to be seen. Flashing lights are permitted but it is recommended that cyclists who are riding in areas without street lighting use a steady front lamp.
I read that as you Must have Front/Rear lights, Rear reflector and Pedal reflectors, but all of the rest (Including Steady front/rear lights are Recommendations only.
TBH only using flashers in the dark is a generally bad idea IMO, Intermittently vanishing from drivers view, only to reappear 2m further on with a blinding flash hardly helps ensure your own safety, but it is still in compliance with the rules so crack on chaps...
Oh and fwiw, bright lights attached to helmets are a pet hate of mine. Just the right height to dazzle all the other cyclists.
Red rear flashers on helmets make perfect sense to me, an up high attention grabber for drivers approaching you from behind, but the number of goons I see with a bright white forward facing helmet light, either on steady death ray or 1000lm flash setting is getting silly...
Forward Helmet lights are for riding through the woods at night, use one on the road and the driver of every car you glance at gets blinded, half these **** are trundling along the pavement anyway, so they've blinded the drivers on the road with me and contributed bugger all to their own safety... Cheers.