The buy-out firms that invested £612m (€879m) in Debenhams three years ago are likely to generate a £2.4bn capital gain – the largest recorded for a UK private equity-backed company.

The capital gain depends on the success of the department store group's initial public offering, which started pre-marketing to potential institutional investors last week. The flotation is expected to value the group at £3bn and is likely to be the largest IPO in the year.