It is an old and not very funny joke: how do you tell if a politician is lying? Their lips are moving. Members of the Senedd, the Welsh parliament, are intent on tackling this age-old problem by bringing in legislation that bans politicians from telling untruths. If the law comes into force, Wales would be the first country in the world to make lying by politicians a criminal offence. The former Plaid Cymru leader Adam Price, who is leading the charge against the liars, said that in a world of post-truth politics, populism, disinformation and deep fakes, and with elections taking place in the UK and US this year, the issue was vital. “The public are rightly tired of seeing certain politicians lie with impunity,” he said. “It is not enough for us as lawmakers to throw up our hands in disgust. We have the power to change the rules so all politicians act with integrity, honesty and respect.” Price has been campaigning on truth and trust in politics since the mid 2000s when he tried to impeach Tony Blair over the Iraq war. He said: “Then it was almost laughed out of court with comments such as: ‘There aren’t prisons big enough’. I think over the course of two decades it’s come from the margins to be seen as a serious proposition. “There’s always been something of a credibility gap in politics but that’s become a gaping chasm. We’re trying to restore what should be a basic principle: that politicians should never deliberately set out to deceive. Hopefully it will set the precedent that could be adopted across democracies around the world.” Welsh politicians are looking at the issue as the Senedd Cymru (members and elections) bill passes through the parliament. It includes plans to increase the number of members and reform the voting system. Price has tabled an amendment calling for it to be made illegal for a Senedd member or candidate to wilfully mislead the parliament or the public. A defence would be that the statement could reasonably be inferred to be opinion, belief or future intention rather than a statement of fact. His amendment was backed by the Liberal Democrats and the Tories. The shadow constitution minister, Darren Millar of the Welsh Conservatives, said: “Untruths and misinformation have been a blight on political discourse in recent years.” The Welsh first minister, Vaughan Gething, has said he backs the “general principle” of the proposal and would like to see it considered by the standards of conduct committee. Several other countries have laws that ban lying in certain circumstances, but Price said the Welsh version would be much more general. The amendment draws on the work of Compassion in Politics. Jennifer Nadel, a co-director of the cross-party thinktank, said: “There are laws that prevent lying in many other professions and areas of public and professional life. Politicians shouldn’t be exempt from the rules that most of us live by. “It can’t be right that the unscrupulous should be allowed to knowingly make false statements to court popularity or win votes without consequence. If we want to rebuild the public’s trust in the political class then preventing deception is a vital first step. If Wales passes this law, we hope that other governments, including that at Westminster, will introduce similar measures.”