Motorists who flash their headlights to warn others of speed cameras ahead could face a £1,000 fine or even a month in prison, as police in England and Wales treat the practice as obstructing officers in their duties.
The gesture, often seen as a friendly tip-off between drivers, is not a standalone criminal offence. However, authorities can pursue charges under Section 89 of the Police Act 1996, which makes it an offence to "wilfully obstruct a constable in the execution of his duty."
Highway Code Rules on Flashing Lights
Highway Code Rule 110 states: "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."
Rule 112 also cautions that the horn should be used "only while your vehicle is moving and you need to warn other road users of your presence" and adds: "Never sound your horn aggressively."
Police Action and Penalties
Given that officers are actively attempting to catch speeding motorists, alerting drivers to slow down temporarily is legally regarded as interfering with police operations. The maximum penalty for this offence is one month's imprisonment or a fine of £1,000. Under sentencing guidelines, punishments can range from a fine and custodial sentence through to a conditional discharge or community order.
Police take a dim view of such behaviour. Evidence of this can be found in the weekly newsletter of a local primary school from earlier in 2026. The newsletter cautioned that "several people are warning other motorists" about the presence of a Cheshire Police speed van that had recently been deployed to monitor traffic outside the school. The school noted that officers were warning this conduct breached both Highway Code Rule 110 and Section 89 of the Police Act 1996, and that they "could charge anyone who appears to be obstructing their ability to conduct speed checks on other motorists by warning them," adding: "The maximum fine for obstructing a police officer is a penalty of £1,000."
Furthermore, the Crown Prosecution Service (CPS), in its official guidance on Public Justice Offences, specifically lists "giving a warning to other motorists of a police speed trap ahead" as an example of conduct that would constitute resisting or wilfully obstructing a constable in the execution of their duty.
The Court Case: DPP v Glendinning
A 2005 case involved a lorry driver who was observed flashing his headlights at oncoming motorists after spotting a speed camera van on a dual carriageway. Officers witnessed this, concluded he was deliberately alerting other drivers and charged him with obstructing police.
The driver was initially found guilty, although the conviction was subsequently overturned at the High Court, where judges ruled that concrete evidence of actual obstruction was required, rather than merely the potential for it to have occurred. In this particular instance, the High Court determined there was no evidence that oncoming vehicles were exceeding the speed limit, that motorists had altered their behaviour as a result of being flashed, or that police enforcement activity had been genuinely disrupted.
Nevertheless, the prosecution serves as a clear reminder that police will not hesitate to take drivers to court for flashing their headlights to alert others to speed cameras ahead.
