top of page

Forensic Toxicology


Members of the Department

Bernard Leddy B.Pharm. M.Sc. Ph.D. C.Chem. C.Sci. M.R.Pharm.S. M.R.Chem.S. M.P.S.I

Professor Alexander Robert Walker Forrest

Stanley Porter BSc. >

Forensic Toxicology and the role of the forensic toxicologist encompasses a broad spectrum of examinations; from measuring and interpreting blood and breath alcohol levels in road traffic offences to interpreting the levels of sometimes obscure poisons in cases of suspected murder. 


Our forensic toxicologists

Forensic Equity boasts some of the UKs leading forensic toxicologists with many years of experience in the analysis and interpretation of levels of the widest possible range of drugs and poisons. All of them have also been authorised as alcohol analysts under the Road Traffic Act of 1981 and are therefore adept at so called ‘back calculations’ (calculating the contribution of post-accident drinking or drinks spiked without the knowledge of the consumer)


Why should you consult a forensic toxicologist?

One example of where seeking a second opinion of an experienced toxicologist could be crucial would be where the prosecution seek to prove that a terminally ill person was murdered by a relative administering a larger than normal dose of the patients own analgesic, but where the alternative defence scenario is that the deceased person passed away naturally from their illness.  


Blood levels of opiate drugs like diamorphine can be difficult to interpret and there may be a very fine line between a palliative and a fatal dose, particularly in patients whose bodily functions are impaired by their illness. These types of cases require interpretation by a highly experienced toxicologist to avoid a potentially innocent and caring relative being unjustly accused.

Drugs and driving

It is not only people accused of the more serious crimes that need the benefit of a forensic toxicologist. Driving under the influence of drugs is an offence where the both the impairment of the driver and the presence of a drug must be proven as there is currently no legislation that defines acceptable or illegal levels of drugs in the blood or urine of drivers. But it may not be that simple. What if when the driver’s urine is analysed and the drug found cannot account for the symptoms of impairment. Can the prosecution proceed? Only an experienced toxicologist can determine if the impairment symptoms match the drug.

Drink Driving Defences

Under the Road Traffic Act of 1988, it is an offence (under section 5) for any person to drive, attempt to drive or be in charge of a motor vehicle with excess alcohol, above a prescribed level, in their system. In most cases where a driver is breath tested and found to be over the legal alcohol limit they will be charged with the offence and either plead or be found guilty of the same.

However, there may be certain mitigating circumstances surrounding the event, which might provide a defence and make a challenge to the prosecution appropriate. Those mitigating circumstances which could form a drink driving technical defence may include: post incident drinking, unwitting consumption of alcohol (as in spiked drinks or consumption of domestic beverages with unexpected alcohol content) and non alcoholic substances on the breath which could affect the breathalyser result and aid a drink driving technical defence.

Drink driving defence - Case example

Driver stopped by police whilst driving home after attending a social gathering at a relative's house. He gives a positive breathalyser test at the roadside, but denies consuming any alcohol. An evidential breath test result shows he is over the legal alcohol limit and he is charged under section 5 of the Road Traffic Act 1988. Whilst at the relative's house the driver had consumed several glasses of iced coffee, which he later finds out was laced with brandy.


How can we help with your drink driving defence?

Our drink driving expert witnesses have many years of experience in alcohol analysis (all previously Home Office authorised) and interpretation of the results of those analyses.


Our forensic scientists can:

  • Review the findings of the prosecution scientist, if one has been involved.

  • Examine the evidential breath test results in the light of the alleged unwitting alcohol consumption.

  • Calculate the possible contribution that the consumption of the alcohol in the coffee could have had on the breath test result, taking into account such factors as, the amounts allegedly consumed and the time interval between consumption and breath test.

  • Address the issue of whether or not the presence of alcohol could have been detectable by anyone drinking the coffee.

Drugs and Driving 

Under the Road Traffic Act of 1988 it is an offence under section 4 for any person to drive or be in charge of a vehicle, whilst impaired through drink or drugs. Unlike in the case of alcohol consumption where there are statutory legal limits for the concentration of alcohol; in a drivers system, no such limits exist in the case of either illicit or prescription drugs. Where drugs and driving is suspected, the finding of a drug (licit or illicit) in a person's body fluids must be backed up by medical evidence of impairment, which could have been caused by that drug, However, just because a drug is present in a person's system doesn't mean that drug could or did cause the alleged impairment.

Drugs and driving - Case example

Person is stopped by police, due to alleged erratic driving behaviour and breathalysed at the roadside. The breathalyser test is negative, but the police arrest the driver on suspicion of being impaired through drugs. Driver examined by a doctor who suggests impairment. Driver blames poor driving and behaviour on being upset over a recent bereavement and denies being impaired. They admit to having previously consumed an antidepressant drug, but deny taking any for the last few days. They provide a sample of their urine, which is sent to the laboratory to be tested for drugs. Low levels of an antidepressant drug detected in the urine sample. Driver charged under Road Traffic Act with driving whilst impaired through drugs.


How can we help?

Our forensic drugs driving experts have considerable experience in the analysis of body fluids for drugs and the interpretation of the results of those analyses.


Our forensic scientists can:

  • Review the findings of the prosecution scientist.

  • Comment on the properties of the drug found in the urine and whether its declared effects could potentially affect driving. Any manufacturer's warnings?

  • Interpret the significance of the levels of drug found in the urine in relation to the alleged impairment.

  • Comment on the finding of the drug in the urine sample in the context of the alleged last consumption several days before the incident.

Drink Driving Defences
Drugs and Driving

Seirous Crime involving Drugs or Poison

The consumption either knowingly or inadvertently of drugs or poisons, their distribution around the body and the effects of their consumption on a particular individual is a very complex subject , requiring expert interpretation. Because of the complex nature of the problem, experts may not agree about what the analytical findings actually mean in any particular case.

Serious crime investigation involving drugs or poisons - Case example

A potentially terminally ill patient, being cared for at home, is receiving regular doses of morphine for chronic pain relief. The patient passes away, but it is suggested that their carer administered a morphine overdose to assist their death. Body fluid samples are taken from the deceased and sent to the laboratory for drugs testing. Morphine and its metabolites are found in those samples, at levels which, in the opinion of the reporting toxicologist, are consistent with a potentially fatal morphine overdose.


How can we help prepare a defence?

Our experts have considerable experience in the analysis of body fluids and organs for the presence of drugs and poisons and the interpretation of the levels of drug or poison found.


Our forensic toxicologist can:

  • Review the findings of the prosecution scientist.

  • Interpret the significance of the levels of drug found in the body fluid samples in relation to the allegation of the administration of an overdose.

  • Comment on whether the levels of drug detected could have been achieved by chronic usage alone.

Serious Crime inv. Drugs or Poison
bottom of page