An ad campaign telling the public that “it’s time to buy” bitcoin has been banned after the advertising watchdog ruled that it was irresponsible and misleading. The high-profile campaign, which has featured heavily across the London underground and the capital’s bus network since December, ran with the strapline “If you’re seeing bitcoin on the underground, it’s time to buy”. The Advertising Standards Authority’s move to ban the ads comes a week after the price of the world’s largest digital currency plunged as much as 30% in a day – to half the record highs of more than $64,000 (£45,256) it reached in mid-April – after a Chinese government crackdown on banks’ use of cryptocurrencies. The ASA received complaints that the ads failed to illustrate the risks involved with investing and trading in bitcoin, which is not regulated in the UK, and was therefore misleading. The watchdog also received a complaint that the ads “took advantage of consumers’ inexperience or credulity”. In its ruling against Luno, the cryptocurrency exchange that is part of a group that also owns CoinDesk, the ad watchdog said the choice to display the advertising on the London underground and buses meant that financial novices were being targeted. The ASA said the simplicity of the “it’s time to buy” statement “gave the impression that bitcoin investment was straightforward and accessible. “We understood that bitcoin investment was complex, volatile and could expose investors to losses,” said the ASA. “That stood in contrast to the ad. The audience it addressed, the general public, were likely to be inexperienced in their understanding of cryptocurrencies.” The ASA banned the ad campaign for breaching the UK code on misleading and irresponsible advertising. Luno said that it would feature an “appropriate risk warning” in future campaigns. In March, the ASA banned a similar-style full page ad in a local newspaper that told readers “there is no point in keeping your money in the bank”, including a testimonial that described bitcoin as “digital gold”. Critics of bitcoin have been predicting a crash in the market for months, with some comparing its meteoric rise to other financial bubbles such as “tulip mania” and the South Sea bubble in the 17th and 18th centuries. Earlier this month, the Tesla chief executive and staunch cryptocurrency supporter, Elon Musk, posted a string of tweets that appeared to show he had made a U-turn on his support for the decentralised coins. Musk suspended plans to let Tesla customers pay for cars in bitcoin because of environmental concerns about the energy required to mine them. “Cryptocurrency is a good idea on many levels and we believe it has a promising future, but this cannot come at great cost to the environment,” he tweeted.