Fears have been raised that authorities like Norfolk County Council are having to pick up the bill to fund the "completely unsustainable" free bus pass scheme.
The county council spends £12m each year to reimburse bus operators for journeys made by older and disabled people who use the pass entitling them to free off-peak travel.
Local government chiefs said the funding Whitehall gives councils to meet those costs is not covering what authorities are paying.
Norfolk County Council said it was unable to determine whether there is a shortfall, because the money it gets from the government is part of a bigger package of cash, rather than specifically to cover those costs.
But the Local Government Association (LGA) calculates total payments by councils to bus companies was £452m higher than the sum they got from government to reimburse them.
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The LGA says it means councils are spending less on other services, such as free peak travel, community transport services, reduced fares and school transport.
In Norfolk, just under 5.2m journeys were made using concessionary bus passes in 2022/23.
The council says, since the Covid-19 pandemic, concessionary bus pass holders have been the slowest to return to buses and the authority has been trying to encourage them back on.
Levels are now back up to around 70pc of pre-pandemic levels.
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Graham Plant, the council's Conservative cabinet member for highways, infrastructure and transport said: "I agree that it is vital the scheme is properly funded – but more importantly, I believe the concessionary travel scheme is extremely important for both our residents and for the continuation of bus services.
"Being a rural county, our bus services are a key part of keeping residents independent and able to get around.
"For bus operators across Norfolk the concessionary travel reimbursements is an important part of their income which enables services to continue to run."
LGA transport spokesperson Linda Taylor said it was "completely unsustainable" to expect councils to prop up the scheme and the scheme should be properly funded.
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