FirstGroup Plc has been cleared by the Competition Commission to buy the new Greater Western rail franchise.
The inquiry looked at competition between bus and rail services
The Commission had considered the effects on competition of FirstGroup running both bus and rail services in the Greater Western area.
Diana Guy, who led the inquiry, said: "Our analysis found only a few routes where there was scope for competition between buses and trains."
The franchise covers the South West, Reading and parts of London.
The final report confirmed the findings of a provisional report from February.
In her report, Ms Guy said FirstGroup would have only a "very small" profit incentive to raise bus fares or alter services in order to shift passengers to trains.
The Commission also concluded the purchase would not reduce the level of public transport provision in the region.