UK online retailer Ocado, long rumoured to be preparing to list in London, is to give some of its shoppers the chance to buy shares in the business.

The company, which is set to issue a prospectus to potential investors in the IPO within the next three weeks, has invited those who have spent over GBP300 (US$435) from the start of the year to buy shares.

"The board of Ocado is considering whether to float Ocado on the London Stock Exchange when the market conditions are right and all other legal, regulatory and other processes are completed," wrote chief executive Tim Steiner.

"If we do decide that the time is right for Ocado to float we will publish a formal 'intention to float' announcement. Should we decide to do this, we would like to offer Ocado customers who have spent over GBP300 with us in the period from 1 January 2010 to the time of announcement the opportunity to buy shares in the flotation."

Ocado has remained coy about any timetable for the flotation. In March, finance director Andrew Bracey told Reuters that Ocado wanted to list after the UK General Election although exact details were not revealed.

Industry watchers have questioned whether Ocado could mount a successful IPO, pointing to other failed flotations in the UK this year, including a planned listing by clothing retailer New Look.

However, successful IPOs in Europe, including that of Danish food ingredients business Chr Hansen, has breathed fresh life into the market.