What a £1,000 Fine Means for Drivers Who Flash Headlights to Warn of Cameras

• Flashing headlights at oncoming traffic is not an offence in itself, but police can charge a warning about a speed trap as obstructing an officer.
• Obstructing a constable carries up to one month in prison, a fine of up to £1,000 or both on summary conviction.
• A 2005 High Court ruling cleared a lorry driver who signalled a speed trap warning, as no driver he warned was speeding or likely to speed.

The Courtesy Flash That Police Can Treat as Obstruction

Most drivers who have seen an oncoming car flash its lights on a dual carriageway know what the signal means. A van or camera sits somewhere ahead, and the stranger in the other lane has just saved you a fine. Dorset Police explained in a statement reported on 3 November that the favour carries a risk for the driver who does it. The force describes warning other drivers of a speed van or camera ahead as obstructing a police officer, an offence that police say can end in a fine of up to £1,000 or a month in prison.

No specific criminal offence of flashing headlights to warn others exists. The charge is obstruction, and it attaches to what the flash is for. A flash to tell another road user you are there is what the Highway Code allows. A flash to tell oncoming cars about a speed van is what officers say they can prosecute.

That distinction rests on three documents: the Highway Code, a section of the Police Act 1996 and the Crown Prosecution Service’s guidance to prosecutors. A fourth source, a 2005 High Court ruling, shows what a prosecution has to prove. Each is covered below, along with what a driver can do instead.

What Rule 110 of the Highway Code Allows

The Highway Code covers headlight flashing in rule 110, which reads: “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.”

The rule gives one purpose and rules out the rest. A flash that tells others you are present fits. A flash that tells them a camera lies ahead, that they can pull out or that they should slow down does not, as each of those carries a message about something other than your own presence. Police read the speed trap warning as a message of exactly that kind.

The criminal charge comes from a different place, and that place sets the penalty.

The Charge Under Section 89 of the Police Act 1996

Section 89 of the Police Act 1996 sets out two offences against a constable. Subsection (1) covers assault and carries up to six months in prison, a fine up to level 5 on the standard scale, or both. Subsection (2) is the one that applies to a warning flash, and the statute reads: “Any person who resists or wilfully obstructs a constable in the execution of his duty, or a person assisting a constable in the execution of his duty, shall be guilty of an offence and liable on summary conviction to imprisonment for a term not exceeding one month or to a fine not exceeding level 3 on the standard scale, or to both.”

Dorset Police puts level 3 at £1,000. The statute page marks the section as applying to England and Wales. Obstruction under subsection (2) tops out at one month in prison, against six months for assault under subsection (1).

The CPS spells out what the charge needs. Its guidance on public justice offences says a person obstructs a constable if they prevent the officer from carrying out their duties or make it more difficult. The obstruction also has to be wilful. In the CPS reading, that means the driver did something on purpose, or failed to act on purpose, with the aim of bringing the obstruction about. Why they did it is beside the point, a rule the guidance takes from the case of Hills v Ellis, reported from 1983.

The CPS gives examples of conduct that can amount to the offence. Two of them involve tipping off a landlord about an after hours drinking inquiry and alerting someone to a coming police search of premises. A third is aimed at drivers: “giving a warning to other motorists of a police speed trap ahead”.

Dorset Police pointed to that entry when it explained its position: “The Crown Prosecution Service (CPS) charging standards actually state, among a list of behaviour, that warning other motorists of a police speed trap ahead would fulfil the offence,” the force said.

The CPS confirms the ceiling of one month’s imprisonment and says the offence goes only to summary proceedings.

A School Gate Warning and Cheshire Police

The warning is not confined to one force’s statement. A local primary school’s weekly newsletter earlier in 2026 said that a Cheshire Police speed van had been positioned to check traffic speeds outside the school, and that “several people are warning other motorists”.

The same newsletter relayed the police response. The school said police were warning that the behaviour breached both rule 110 of the Highway Code 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”. The newsletter added: “The maximum fine for obstructing a police officer is a penalty of £1,000.”

The report of the newsletter records no charge. It records police telling a school where they stand, and it matches what Dorset Police explained.

The 2005 Case That Shows What Prosecutors Must Prove

The most useful piece of law for a driver is a decision that went the driver’s way. On 13 June 2004 a lorry driver on the A303 dual carriageway in Somerset approached a police car parked in a lay-by with a speed camera and signalled to the traffic behind him to slow, using his right hand out of the cab window. Police concluded he was warning the motorists behind him of a speed trap. South Somerset Magistrates’ Court convicted him of obstructing a constable.

The Crown Court at Taunton heard his appeal and threw the case out at the close of the prosecution evidence. Police video showed nobody speeding, and nothing showed anyone reacting to the signal. The Director of Public Prosecutions took the case to the High Court, where Lord Justice Scott Baker and Mr Justice Owen dismissed the appeal on 13 October 2005. Mr Justice Owen held: “There could be no obstruction of the officers in the exercise of their duty unless there were vehicles that were speeding or were likely to speed.” Lord Justice Scott Baker agreed and found no actual obstruction of the police.

The driver in DPP v Glendinning used his hand, not his headlights, but the question the court answered covered any warning of the presence of a speed trap. The judgment also recalls the 1910 case of Betts v Stevens, in which a patrolman who warned drivers already breaking the speed limit was convicted.

Read with the CPS wording, the two point the same way. The CPS definition turns on an officer being prevented from doing the job or finding it harder, and the High Court wanted proof of drivers who were speeding or likely to speed. A charge needs an officer who saw the warning, a driver who plainly meant it and evidence about who received it.

The ruling does not make the practice safe. Dorset Police, the CPS and the Cheshire officers all still list the warning as conduct that can be charged, and the 2005 decision gives a driver a defence to argue, not an exemption.

What to Do Instead of Flashing

The simplest fix costs nothing: do not flash to warn of a camera or a van. The reliable way to avoid a speeding penalty is a speedometer that reads at or under the limit, and a driver who does that has no use for a warning. The guide to how penalty points and motoring offences work sets out the penalties for speeding itself.

How much room police leave before a camera records a driver is a separate question. The report on speed camera tolerance rules answers it.

A driver who is caught can look into a speed awareness course in place of the fine, and qualifying is getting harder.

A driver who receives a flash from an oncoming car has done nothing wrong, and the sensible response is to check the speedometer and ease down to the limit.

For your own headlights, rule 110 is the guide: flash to let other road users know you are there and nothing more. If an officer raises the matter with you, the CPS test and the 2005 ruling set the two questions, which are whether the act was deliberate and whether it obstructed the officer. Anyone facing a charge should take legal advice before answering.

The Dorset Police statement, the CPS list and the Cheshire school notice point the same way. The offence comes from a 1996 Act, and police are restating it for drivers who flash. A driver who stops loses nothing but the habit.

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Sources

• legislation.gov.uk: Police Act 1996, section 89
• Crown Prosecution Service: Public Justice Offences incorporating the Charging Standard
• National Archives: Director of Public Prosecutions v Glendinning, 2005 EWHC 2333
• Daily Mirror: Police end debate on flashing headlights to warn of speed camera

Reviewed by Preetam Gadekar