Drug Driving in the UK: 10 Years On
Drug driving became a criminal offence in the UK in 2015 with the introduction of new laws aimed at tackling the growing issue of impaired driving due to illegal and prescription drugs. A decade later, the impact of these laws is still a subject of debate. Have they been effective in reducing drug-related accidents and deterring offenders, or have they led to unforeseen legal and societal challenges?
This blog explores the journey of drug driving laws in the UK, from their inception to their impact today. We will cover the reasons behind their introduction, the legal limits, the effectiveness of the law in preventing offences, and the best legal defences available to those accused of drug driving.
1. Why Drug Driving Became an Offence in the UK?
Before 2015, the UK had laws against driving while impaired by drugs, but proving impairment was a complex and subjective process. Unlike alcohol, where legal limits and breathalysers provided clear-cut evidence, drug impairment was harder to measure and prosecute.
- The Rise of Drug-Impaired Driving
Studies in the early 2010s showed an increase in drug-related accidents. The Department for Transport (DfT) and police forces reported cases where drivers under the influence of drugs caused serious and fatal collisions. Cannabis, cocaine, and prescription medications such as diazepam and morphine were frequently detected in drivers involved in accidents.
- Public Safety Concerns
Campaigns from road safety organisations, families of victims, and law enforcement highlighted the dangers of drug-impaired driving. Unlike alcohol, where a drink-driving culture had been challenged for decades, drug use behind the wheel was often underestimated. There was also concern that users of prescription medication might be unknowingly breaking the law.
- Government Response
In response, the UK government introduced specific drug-driving laws under Section 5A of the Road Traffic Act 1988, which made it an offence to drive with certain drugs in the bloodstream above prescribed limits. This law removed the need to prove impairment – instead, exceeding the legal threshold was enough for prosecution.
2. What Are the Legal Limits?
The law introduced strict limits for both illegal and prescription drugs. These limits were set based on scientific studies determining the point at which drugs impair driving ability.
Illegal Drugs:
For illegal substances, the limits were set extremely low to reflect a zero-tolerance approach:
- Cocaine – 10µg/L
- Cannabis (THC) – 2µg/L
- Ketamine – 20µg/L
- LSD – 1µg/L
- MDMA (Ecstasy) – 10µg/L
- Heroin – 5µg/L
Prescription Drugs:
For prescription medication, limits were set higher to account for medicinal use:
- Diazepam – 550µg/L
- Methadone – 500µg/L
- Morphine – 80µg/L
- Temazepam – 1000µg/L
- Clonazepam – 50µg/L
However, the law allows a medical defence if the driver can prove they were using the drug as prescribed and were not impaired.
How Are Drivers Tested?
Police now use roadside saliva swabs and blood tests to detect drug use. If a driver tests positive, they are taken for a blood test at a police station, which provides the evidence needed for prosecution.
3. Has the Drug Driving Law Reduced Offences or Made Them More Problematic?
A decade after its introduction, the effectiveness of drug-driving laws remains a mixed picture. While there have been notable successes in enforcement and awareness, concerns remain about whether the law has achieved its goal.
- Increased Arrests
Since 2015, drug-driving arrests have risen significantly. In some regions, the number of drug-driving offences now exceeds drink-driving. Police report that roadside testing has helped catch offenders who might previously have escaped detection.
- Impact on Road Safety
According to DfT statistics, drug-related road accidents have decreased in some areas, suggesting that enforcement has had a deterrent effect. However, national accident statistics still show drug impairment as a factor in fatal crashes, raising questions about whether the law has been a sufficient deterrent.
- Repeat Offenders and Drug Trends
Despite tougher enforcement, many cases involve repeat offenders. Some drivers, particularly those dependent on drugs, continue to take the risk. Additionally, the rise of new psychoactive substances (formerly called legal highs) has created new challenges, as these drugs may not always be covered by existing limits.
- Concerns Over Prescription Drug Users
One of the unintended consequences of the law is confusion among prescription drug users. Some legal medication users have been unfairly penalised because they were unaware of the limits or did not have the correct medical documentation.
- Racial and Socioeconomic Disparities
There have been concerns about potential biases in enforcement. Studies suggest that certain groups—particularly young men and individuals from lower-income backgrounds—are more likely to be stopped and tested, raising concerns about fair application of the law.
- Public Awareness
Unlike drink-driving, which has been a focal point of public safety campaigns for decades, drug-driving awareness is still growing. Many people are unaware of how long drugs remain in the system, leading to accidental offences.
4. The Best Defences Against Drug-Driving Charges (With Examples)
If charged with drug driving, there are several legal defences that may apply. The outcome of a case depends on the circumstances, the evidence presented, and the quality of legal representation.
1. Medical Defence
Drivers who have tested positive for prescription medication can argue that they were taking the drug as prescribed and were not impaired. To succeed, they must provide:
- A valid prescription
- Medical evidence showing they took the correct dosage
- Proof that they were fit to drive
Example: John, a 45-year-old professional, was pulled over for a routine traffic stop. A roadside drug test detected high levels of morphine in his system. However, John had a valid prescription for morphine due to a back injury and had been taking the medication as directed by his doctor.
In court, his solicitor presented:
- His prescription records proving lawful use of morphine
- A doctor’s letter confirming that he was on a stable dosage and fit to drive
- A toxicology report showing that while the drug was in his system, it was within therapeutic limits
The court accepted his medical defence, and he was acquitted.
2. Unreliable Testing
Drug tests, particularly saliva swabs, are not always accurate. If there were errors in the testing procedure, or if the sample was contaminated, the results could be challenged.
Example: Sarah was stopped by the police after they suspected she was driving erratically. A roadside saliva test showed positive for cocaine, and she was arrested. However, her solicitor later discovered that:
- The testing kit used was past its expiry date, making the results unreliable.
- The police failed to follow standard procedure when handling her sample, increasing the risk of contamination.
- A subsequent blood test came back negative, contradicting the saliva test.
Based on these findings, her case was dismissed due to unreliable evidence.
3. Rising Blood Drug Levels
Unlike alcohol, drugs do not metabolise at a consistent rate. A driver might argue that their drug levels were below the limit while driving but increased by the time they were tested at the police station.
Example: Michael, a 30-year-old taxi driver, had smoked cannabis the night before his shift. He believed it had cleared from his system by the time he started work. However, he was stopped by police, and his blood test at the station showed THC levels above the legal limit.
His solicitor argued that:
- His THC levels were likely below the limit when he was actually driving.
- THC can remain in the bloodstream for extended periods, and the delay between his arrest and blood test could have caused a false positive.
- He provided toxicology expert evidence demonstrating how THC levels fluctuate post-use.
Due to reasonable doubt about his impairment at the time of driving, the case was dropped.
4. Spiked or Passive Ingestion
Some drivers claim they unknowingly consumed a drug—for example, through passive cannabis inhalation or spiked food or drink. Although this defence is difficult to prove, forensic evidence and witness testimony may support it.
Example: David attended a party where he unknowingly consumed a brownie containing cannabis. He later drove home, unaware that he had consumed any drugs. The next morning, he was stopped for a minor traffic violation and tested positive for THC.
In his defence, his solicitor presented:
- Witness evidence from partygoers confirming that he was unaware of the cannabis in the food.
- A toxicology expert report explaining how THC can remain in the bloodstream long after ingestion.
- The fact that he had no prior drug-related offences, supporting his claim that he would not knowingly drive under the influence.
While difficult to prove, the court ruled in his favour due to reasonable doubt.
5. Lack of Legal Procedure
Police must follow strict procedures when conducting drug tests and arrests. If officers failed to follow protocol—such as not waiting the required time before administering a test—the evidence might be deemed inadmissible.
Example: Emily was stopped at a checkpoint and asked to provide a saliva sample. The test came back positive for benzodiazepines, and she was arrested. However, her solicitor found serious procedural errors in her case:
- The police did not inform her of her right to legal advice before taking the sample.
- The officer who conducted the test was not trained in using the equipment.
- The required 20-minute observation period before administering the test was not followed.
Due to these procedural failures, the judge ruled the evidence inadmissible, and Emily’s case was dismissed.
6. No Proof of Driving
In some cases, a person may be charged without clear proof that they were driving at the time. For example, if a driver is found asleep in a parked car while over the limit, they may be able to argue that they were not intending to drive.
Example: Tom had been drinking and smoking cannabis at a friend’s house. Knowing he was over the limit, he decided to sleep in his car, parked in a layby. A passing police officer saw him in the driver’s seat with the keys in the ignition and assumed he had been driving under the influence.
At trial, Tom’s solicitor successfully argued:
- He was not driving and had no intention of doing so until he was sober.
- The prosecution failed to provide evidence that he had driven the car while impaired.
- He had taken reasonable steps to avoid driving, such as sleeping in the back seat with the keys out of reach.
Since there was no concrete proof that he had driven under the influence, he was found not guilty.
Head over to our YOUTUBE channel below to see our Senior Solicitor, Conor Johnstone, discussing drug driving and the possible defences.
Conclusion: Where Do We Go From Here?
Ten years after its introduction, the UK’s drug-driving law has had a significant impact, leading to increased arrests and improved enforcement. However, challenges remain, including high reoffending rates, concerns over fairness, and the difficulty of distinguishing between legal and illegal drug use.
Looking ahead, further measures may be needed, including:
- Better public education on the dangers and legal risks of drug driving.
- Improved roadside testing to ensure accuracy and fairness.
- Greater support for prescription drug users to prevent wrongful convictions.
- Stronger rehabilitation programs for repeat offenders.
While the law has made progress, drug driving remains a serious issue. Continued enforcement, education, and reform will be crucial in making UK roads safer over the next decade.
