The company yesterday said it had held "very preliminary" talks over a potential tie-up with "all or part" of Keolis, which is 44.5 per cent owned by SNCF.
Keolis – which has the largest bus and coach fleet in France – employs 40,000 staff with operations in Europe, Algeria, Australia and Canada.
In the UK, it is a minority shareholder in the Govia joint venture with Go-Ahead, which operates the Southern, Southeastern and London Midland rail franchises.
Arriva stressed that talks were at an "exploratory stage", with no certainty of any agreement.
The combination of the two businesses would create a transport giant with revenues of almost 6 billion – and throw down the gauntlet to the UK's current biggest transport firm, Aberdeen-based FirstGroup, which had revenues of 6.2bn in the year to March.