Labour is buying targeted online adverts attacking the Lib Dems for wanting to decriminalise drugs, The Independent has learned.
Keir Starmer's party in mid-April began to buy Facebook and Instagram attack ads singling out the policy to tens of thousands of people.
It comes as the opposition ramps up authoritarian rhetoric and policies on social issues like climate protests and criminal justice.
In January Keir Starmer said he was not in favour of changing drug laws - putting him at odds with mayor of London Sadiq Khan, who wants to pilot new approaches in the capital.
Facebook's ad library, which keeps a record of ads purchase, shows Sir Keir's party started to buy the adverts in the run-up to local elections next month May.
The Lib Dems say they want want to take a public health approach to drug addiction, treating it as medical issue rather than criminal.
They also say they would give people who need it access to medical cannabis and regulate sales of it market.
But the Labour ads falsely claim Ed Davey's party wants to "legalise drugs", a different policy.
One version of the advert says "The Lib Dems want to legalise drugs and soften punishments" as well as "get rid of nuclear weapons", next to a picture of Ed Davey.
A second version features the text "LEGALISE DRUGS" on a yellow background, next to a headline clipped from The Independent.
The headline, which is actually from 2015 when Nick Clegg was leader, says "All drugs should be decriminalised, say the Lib Dems" – not supporting the claim in the rest of the advert.
The anti-decriminalisation push comes weeks after Labour called for a nationwide ban on climate protests on roads and around oil depots.
A spokesperson for Labour left-wing pressure group Momentum described the adverts as "morally disgraceful, politically inept".
"The public actually support liberalising our drug laws and ending the failed War on Drugs," they said.
"But if you conflate the public with Fleet Street, you'd never know it."
A poll by YouGov conducted last year found that by 52 per cent to 32 per cent UK voters would support the full legalisation of cannabis.
Facebook allows adverts to be targeted by demographics and location, meaning parties can say one thing to one set of voters and another to another set.
A Liberal Democrat spokesperson said: "Instead of pushing false claims about the Liberal Democrats, Labour would do better to focus on the Conservative government's appalling record on crime, which is seeing 5,000 crimes go unsolved every day.
“Liberal Democrats are calling for proper community policing, where officers are visible, trusted and focused on cutting crime.
"These local elections are a chance to elect Liberal Democrat councillors who will work hard to prevent crime and make sure people can truly feel safe in their communities.”
