The largest shareholder in National Express has joined forces with a private equity firm to table a takeover approach for the beleaguered transport business.
Spain's Cosmen family, which owns 18.5% of National Express, is working with buy-out firm CVC on the potential deal.
The UK's biggest transport firm, FirstGroup, pulled out of a possible takeover on Wednesday citing "uncertainties" over the business - but National Express said at the time it had received another approach from an unnamed third party.
CVC confirmed the speculation in the Financial Times today but did not comment on reports that the interest valued National Express at £500 million.
The Cosmens took their stake in 2005 when National Express entered the Spanish coach and bus market with the acquisition of Alsa, which was owned by the family.
Jorge Cosmen is currently deputy chairman of the UK firm, which employs 43,000 people through operations in the UK, North America and Spain.
CVC said in a brief statement that an indicative proposal had been made to the board of National Express. Shares were almost 8% higher after the statement.
CVC is said to have written to the board three days ago, although National Express is looking for an offer of around 400 pence - more than £600 million - before engaging with any bidder, the FT says.
Earlier this month, National Express was forced to walk away from its loss-making East Coast rail deal after failing to renegotiate the franchise with the Government.
The firm, which is almost certain to hand over the franchise to the Government by the end of the year, has been warned it could lose its two other rail franchises - East Anglia and London commuter service c2c.
National Express is also labouring under a £1.2 billion debt mountain.
Rival transport groups Stagecoach and Go-Ahead are also said to be considering their options over a possible bid but have yet to approach the company, the FT says.