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By Katy Austin
Business correspondent, BBC News
An increasing number of people are getting behind the wheel after using cannabis and cocaine, according to one of Britain's top police officers.
Chief constable Jo Shiner of the National Police Chiefs Council said there was a "social acceptance" particularly among younger people.
Some forces made more arrests for drug-driving than drink-driving during December crackdowns, the BBC has found.
The Ministry of Justice said it was clamping down on the behaviour.
The National Police Chiefs Council (NPCC) has released new arrest data following a campaign of roadside testing in December. It suggested that in England and Wales 48.5% of drug tests were positive, while 9.5% of breath tests for alcohol were positive.
Merseyside Police said it regularly catches more drug drivers than those over the alcohol limit and the problem is "highly prevalent".
The BBC joined Merseyside officers on a roadside testing operation in Liverpool on Tuesday morning.
Within half an hour, preliminary drug wipe tests had detected cannabis or cocaine in the systems of three drivers. They were also breathalysed but weren't over the limit for alcohol.
All three were arrested and taken into custody for a blood test, which will determine whether they face further action.
'Whole life destroyed'
Summer Mace, a 24-year-old trainee teacher from King's Lynn, knows all too well the devastating impact drug driving can have.
In January last year her mother, sister and stepfather were killed in a head-on collision with a driver who was under the influence of illegal drugs, just a few miles from their home.
Now, Summer describes her life as a waking nightmare: "The moment those people are gone, your whole life has just been destroyed. It's absolutely shattered into a million pieces."
She wants tougher sentences for anyone caught drug driving, even if they don't cause an accident.
"If you have a harsh sentence that puts someone away, the moment they drug drive, that is going to deter people. But people…. just get a driving ban and a bit of a fine. They're not going to care."
Chief Constable Shiner also said stronger sentences were needed, particularly where someone was killed or seriously injured.
A Government spokesperson said: "We have tough penalties and rigorous enforcement in place to screen suspected drug drivers at the roadside, and people found guilty of causing death by careless driving when under the influence of drugs can now face a lifetime prison sentence.
It said its 10-year drug strategy would "further help clamp down... by tackling the supply of illicit drugs whilst building a world class system of treatment for those who abuse drugs to help turn their life around."
'Less stigma'
Roads policing inspector Gavin Dixon said 85-90% of these forensic tests - which currently take at least four weeks to come back - do show a level of drugs above the limit.
He does not think there is yet the same social stigma around driving after taking drugs, compared with alcohol.
"I think people don't realise it's stays in your system as long [as it does], they don't think the police are out catching drug drivers. The reality is we are."
Insp Dixon said: "Over the last few years we've seen year on year increases. Last year we arrested 2,700 people for drug driving, one of the highest in the country. And I think that's because of the effort and resources we've put into it."
Merseyside police recorded a particularly high number of drug driving arrests during its December Operation Limit campaign - 469, compared to 191 for drink driving.
The NPCC figures did not give a breakdown of drug and drink driving arrest by region so the BBC approached individual forces for their December figures.
Other police forces where drug-related arrests exceeded those for drink driving include Hampshire, Thames Valley, Greater Manchester, Sussex and North Wales.
'Social acceptance'
Jo Shiner, the NPCC's Road Safety Lead, said: "We're definitely seeing more people who are driving under the influence of drugs. And there seems to be a social acceptance between those groups who do that, that it's okay. It's absolutely not."
She added that it was notable among younger drivers: "I think generally in society we're seeing more use of cannabis, for example, and we are definitely seeing that when we are stopping and testing drivers."
Since 2015 in England and Wales - a few years later in Scotland - it's been an offence to drive with above certain limits of specified illegal or prescription drugs. The law change was designed to make it easier to catch and convict drug drivers, and enabled roadside testing.
It was brought in after a campaign by the family of 14-year-old Lillian Groves, who was killed by a speeding driver who had smoked cannabis.
People convicted of drug driving may end up with a driving ban of one year or more, a fine, and up to 6 months in prison. Causing death by careless driving under the influence of drugs can carry a life sentence.
Katie's partner and dad of her three children Sam Morris was killed in a drug driving collision, she doesn't think people take risks of drug driving, and dangerous driving in general, seriously enough.
"The impact Sam's death has had on us as a family is unmeasurable and continues to unfold as time passes, our daughters are so young that as they grow new questions are asked", she said in a statement to the BBC.
"I believe that if you cause a death while driving unlawfully whether that is through drink or drugs or any other reason it should be treated as manslaughter.
"The laws around this need to change to bring a small amount of peace to my families like mine and hopefully deter anyone from getting behind the wheel when they are unfit to do so," Katie added.
Additional reporting by Adrian Bradley and Hope Rhodes.