Simon Posner, director general of the Confederation of Passenger Transport (CPT), believes a combination of rising staff, energy and vehicle costs are forcing operating companies to raise the fares they charge customers.
"We're trying our best of course to keep the fares down because that's the way we get passengers on to our vehicles, but some of it has to be passed on," he said on the Today programme.
"If we can work with local authorities to give priority to bus passengers on the road people will leave their cars at home, they will get on the bus, and that's what will get the change. Fares are important, but priority for bus passengers is what would really get them to change."
Rising congestion on Britain's roads had led to increased calls for more people to use public transport.
Some political parties including Labour propose introducing a road charge to deter motorists from making unnecessary journeys. Others prefer a more direct solution: one of the main planks of the Scottish Socialist Party's manifesto for the forthcoming Scottish elections is its support for introducing free public transport north of the border.
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