OECD Secretary-General Angel Gurria told CNBC that Brexit proponents in the United Kingdom were allowed to hijack the narrative ahead of the 2016 referendum, wrongly distributing “fairy tale” ideas of what the country would look like after leaving the EU.Speaking to CNBC’s Geoff Cutmore on Thursday at the IMF and World Bank annual meetings in Washington, D.C., he took aim at former U.K. leader David Cameron and his remain campaign, calling it an “exercise in how not to do things.””I think the idea of calling a referendum, or offering to call a referendum, was not very wise,” he said of Cameron’s 2015 general election pledge.”Then you decide to have a referendum — then make sure you win it. And I can tell you it looked like they were electing the prom queen rather than looking at the future of the United Kingdom,” he added.Gurria, who heads a group of advanced economies known as the Organisation for Economic Co-operation and Development (OECD), said that the pro-EU campaigners lost the 2016 vote because “we let the fairy tales, we let all these assumptions about migration and regulation and about everything else, take over the narrative rather than lead the narrative.”Brexit, a highly divisive issue that still rumbles on in the U.K., was backed by a majority of 52% to 48% in June 2016. The campaign featured allegations of fear-mongering and erroneous claims of extra spending on the health service. Attempts to prosecute Boris Johnson, the current prime minister and Brexit supporter, have been thrown out of court, however.Pro-Brexit protesters demonstrating in central London.Steve Taylor | SOPA Images | Getty ImagesCameron, meanwhile, has stayed quiet since the vote but recently defended his actions in a TV documentary, saying that the Brexit vote was “inevitable” due to the strength of feeling inside the country.With a previous Brexit deal being rejected three times by the U.K Parliament, negotiators struck a new deal on Thursday which will now be put in front of the House of Commons on Saturday.Gurria told CNBC that he was “very encouraged” by the new agreement and called on U.K. lawmakers to approve it and move forward. “We believe that it is going to happen,” he added.