The fundraising, which is expected in the first half of next year, is likely to be the last round before the mobile app-based bank floats on the London Stock Exchange. Atom, headquartered in Durham, England, has been forced to delay its initial public offering this year as a result of a tough market environment, which has led to a number of companies shelving their IPOs. Atom is hoping to float in 2024 once the new shareholders are on board, the person familiar with the bank’s plans said.