The legacy of a teenager killed outside her home by a speeding driver on cannabis will live on after her parents achieved a law change in her name.

From today, drivers will be prosecuted if they are caught exceeding new legal limits which have, for the first time, been laid down for eight illegal drugs and eight prescription drugs.

Police are now able to use "drugalysers" to screen for cannabis and cocaine at the roadside.

And officers are also able to test for drugs including ecstasy, LSD, ketamine and heroin at a police station, even if a driver passes the roadside check.

The offence of driving with these drugs in your body carries a maximum six month jail sentence, maximum £5,000 fine, and automatic 12 month driving ban.

The law change comes after tireless campaigning by the family of Lillian Groves to introduce drug testing by the roadside.

Lillian died in 2010 after being struck by a car being driven by John Page near her home in Headley Drive, New Addington, on her mother’s birthday, June 26.

Cannabis was found in Page's system, and there was a half smoked joint on the floor of the car, but there was not enough to charge him with causing death by careless driving while under the influence of drugs, which carries a maximum 14-year sentence.

He was sentenced at Croydon Crown Court to eight months imprisonment in July 2011, and was told by the judge he would serve half of this in prison.

If Page had been tested at the roadside, enough cannabis may have been found to charge him with the more serious offence.

Lillian’s mum, Natasha Groves, said: "We have fought tirelessly since losing Lillian, and our determination has brought about this significant change.

"It has been a tough and emotional journey for us all.

"Lillian is not the only one to have lost her life through the ignorance, arrogance and stupidity of those who mix drugs with driving.

"Those who continue to drive while on drugs now have so much to lose.

"We have achieved this law change in Lillian’s name and her legacy will live on and our roads will be that bit safer."

"The legislation is now up to date and fit for purpose.

"Having to prove impairment will no longer be a matter of judgement, but a testable fact."