Shares in Darktrace have surged after the British cybersecurity firm made its debut on the London Stock Exchange. The Cambridge-based company began conditional trading on Friday at 250p a share, with enthusiastic investors immediately pushing up its stock by 40% to 350p a share, and sending its market value up from £1.7bn to almost £2.4bn. The 250p float price was at a lower level than originally intended, in part to avoid a repeat of Deliveroo’s opening-day flop last month. The company, which uses artificial intelligence to create digital security products to keep businesses one step ahead of hackers and viruses, will raise £143m from the float, with existing shareholders selling shares worth £21.7m. About £25m more could be raised through an overallotment option if there is enough demand from investors. “This milestone marks an exciting day for Darktrace,” said Poppy Gustafsson, the firm’s 38-year-old chief executive. “Our company is deeply rooted in the UK’s tradition of scientific and mathematic research, so we are especially proud to be listing on the London Stock Exchange.” Gustafsson, who opted not to sell any shares in the IPO, holds a 0.4% stake, worth more than £9m at the 330p closing price on Darktrace’s first day of trading. Darktrace was founded in 2013 by mathematicians from the University of Cambridge, artificial intelligence experts and cybersecurity specialists from GCHQ. The British tech billionaire Mike Lynch’s Invoke Capital was Darktrace’s first and largest shareholder. However, his association with the business has caused controversy as he is fighting extradition to the US, where he is accused of fraudulently inflating the value of the British software group Autonomy before its £8.4bn sale to Hewlett-Packard in 2011. Lynch, who co-founded Autonomy and was its chief executive, could face a maximum prison sentence of 25 years if found guilty. He denies any wrongdoing. The flotation of the company has made the 16.2% stake held by Lynch and his wife, Angela Bacares, worth £367m at close. They did not sell any shares as part of the flotation, and are Darktrace’s second largest shareholders. Gustafsson did not shy away from acknowledging the connection at Darktrace’s debut on Friday. “We owe much gratitude to the Invoke team for their pivotal role in the vision, technology, positioning and operational input in the early years, without which today’s success would not have been possible,” she said. The share price bounce after the start of trading indicates that there are plenty of investors willing to back Darktrace’s business prospects despite its association with Lynch, according to analysts. “The listing valuation was nearly half that of original estimates as investors were clearly nervous about the company’s links to Lynch,” said Russ Mould, an investment director at AJ Bell. “The surge in the share price post listing would suggest there are other investors who are more comfortable with the risks and are just focusing on Darktrace’s potential to grow fast in the cybersecurity space.”