One of the two remaining bidders for is reportedly close to dropping out.

The sale was described by City insiders as having been “turned into a train wreck” as prospective buyers baulked at the £500 million price tag, the Mail on Sunday reported.

Exponent Private Equity is attempting to sell the online rail ticket retailer and information provider with interested parties said to include Priceline and private equity firm Kohlberg Kravis Roberts.

Adviser NM Rothschild, which is handling the sale, faces the prospect of a cut-price deal or having to pull the sale, the newspaper reported.

Exponent bought the company for £163 million in 2006 from Virgin backed by £116 million debt. posted a £29 million profit on revenues of £1.1 billion in the year to March 2011.