Teenagers as young as 16 should be allowed access to sexually explicit material, Liberal Democrat delegates have agreed.
Lib Dems are seeking to allow over-16s more freedom
Don Foster, the party's culture spokesman, says they should also be able to visit sex shops and buy pornography - a plan overwhelmingly supported by the Lib Dems spring conference.
The move would end the "twilight zone" between childhood and adulthood where they can have sex, lawfully marry and have a baby at 16 but cannot watch sex, he said.
But the policy was branded "irresponsible" by the Tories.
Lib Fellow MP Steve Webb tried to keep the age at 18, but the proposal was rejected by the conference.
However, delegates backed calls for a ban on material which exploits unlawful acts involving youngsters under 16.
Mr Foster made the case for allowing 16-year-olds to view pornography during a censorship and freedom of expression debate.
While he had worried the proposals would encourage pornography into schools, "the reality is sexually explicit material is already readily available to 16 and 17-year-olds on the internet", he said.
"Our current policy on censorship and freedom of expression is not only out-of-date, it's inconsistent and it's confusing," Mr Foster said.
"We still do not allow 16-year-olds to watch sex, despite the fact they can currently have sex, lawfully marry and indeed, a woman may choose to have a baby at 16.
"This certainly seems out of date given that as Liberal Democrats, we would extend to 16-year-olds full political and social rights ...
"The proposals are intellectually sound - 16 and 17-year-olds in this country are living in a twilight zone between childhood and adulthood, having lost their children's rights, yet only gaining adult rights in a piecemeal fashion, some at 16, some at 17, some at 18.
"This motion merely proposes consistency on the suitable age for obtaining adult rights in line with the well-established Liberal Democrat policy on 16 as the common age of majority."
However, Steve Webb insisted his amendment to keep the age of viewing porn to 18 was not about "prudery".
He said he was concerned about how children younger than 16 could be stopped from getting hold of the material if the age was lowered.
Tory party co-chairman Dr Liam Fox also criticised the move.
"This irresponsible policy is likely to lead to the exploitation of young people and it adds to the many ridiculous policies the Liberal Democrats have dreamed up over recent years," he said.
"With all the problems facing Britain the Liberal Democrats have once again chosen to focus on the absurd."
During the debate, Mr Foster argued that people involved in sexually explicit films should be covered by employment, health and safety laws and be aware of their rights.
He said empirical evidence that pornography leads to acts of violence "is misleading".
Local authorities should retain powers to refuse a licence if a shop has offensive window-displays, allows under 16s to enter or fails to warn customers of the nature of the establishment.
But, Mr Foster said, the Lib Dems would not be legalising films showing bestiality, snuff movies or depict under-16s in a sexually explicit way.
Meanwhile, Lib Dem activists supported proposals to abolish the law of "blasphemy" and instead introduce measures to tackle all forms of discrimination.