from the high way code
"110
Flashing headlights. Only flash your headlights to let other road users know that you are there. Do not flash your headlights to convey any other message or intimidate other road users.
111
Never assume that flashing headlights is a signal inviting you to proceed. Use your own judgement and proceed carefully.
112
The horn. Use only while your vehicle is moving and you need to warn other road users of your presence. Never sound your horn aggressively. You MUST NOT use your horn
* while stationary on the road
* when driving in a built-up area between the hours of 11.30 pm and 7.00 am
except when another road user poses a danger."
http://www.direct.gov.uk/en/TravelAnd ... ort/Highwaycode/DG_070289Personally I find someone coming up behind me and flashing their lights intimidatory and aggressive - OBVIOUSLY I wouldn't be there if i had a choice and as soon as I judge it to be safe to do so I will be out of the way...
in theory flashing lights at someone can be taken as road rage and charged as common assault....common assault is defined as "It is committed by a person who causes another person to apprehend the immediate use of unlawful violence" - hence you don't have to HIT anyone merely give them cause to think you might (if you do then its battery...at minimum)