The manifesto adds that the Liberal Democrats "continue to believe that there is no deal as good for the United Kingdom outside the European Union as the one it already has as a member".
Mr Farron said the drug was a "gateway to harder drugs", and "if you brick up that gateway by making sure that people who are buying cannabis are only buying it from a regulated source then you take away the option to go into harder drugs".
Britain's Liberal Democrats party published its manifesto on Wednesday, including a commitment to work towards outlawing caste discrimination and re-introducing a post-study work visa for graduates in science, technology, engineering and mathematics.
As part of their spending package, the Lib Dems are pledging to axe the freeze on benefits which means they lose value as inflation rises.
Tim Farron's party has been struggling to gain traction as the "party of Remain" in an election campaign where the two main parties have largely avoided addressing the specifics of Brexit.
Mrs May's decision to pull Britain out of the single market was not on the ballot paper past year and any final Brexit deal should be subject to a second referendum, he said.
DESPITE the party only finishing with the fifth highest number of votes in the 2015 General Election in Stroud, the Liberal Democrats' new candidate for the constituency is confident of winning a seat in Parliament.
As well as extra investment for schools and hospitals the Lib Dems are also committed to a £100bn infrastructure investment to help build 300,000 homes a year. "And when it blows up it is going to take our NHS and our schools down with it".
Mr Farron has already said he expects a big Conservative win on 8 June, but his pitch to voters is that his party can help mitigate the effects of Brexit.
'Not Theresa May's cold, mean-spirited Britain'. "I think people feel that we have gone in the wrong direction and they sometimes wish they had someone like Bernard to stand up for them, I'm trying".
One of the most attention-grabbing of these is a proposed ban on diesel auto and small van sales, which the Lib Dems would introduce by 2025.
Elsewhere in the manifesto the Lib Dems said it wants to expand the "Financial Conduct Authority's remit to include a statutory duty to promote financial inclusion as one of its key objectives".
The main opposition Labour party has 31% while the Lib Dems lag behind on 9%, according to the survey of 1,630 people.
And they would also ensure ensure no schools lose money as a result of a new funding formula.
"Research over the last 10 years has suggested that it can have serious consequences for people, such as the development of an enduring psychotic illness, particularly in those who are genetically vulnerable", the Royal College of Psychiatrists has warned.
The manifesto, launched by leader Tim Farron on 17 May, outlines an ambition to build 300,000 homes a year, which is nearly double the current number.
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