Bus company Stagecoach said a bus driver who left a disabled passenger on a bus at a Manchester depot has been disciplined.
The man, 60, was left in his wheelchair until 3am when he was found by a cleaner.
A spokesman for the firm said they are "absolutely committed to helping customers, particularly passengers with disabilities."
"We were very concerned to hear about this case when it was brought to our attention at the time.
All of our drivers are given very clear instructions that part of their job is to check the bus at the end of their shift.
This was an individual oversight and the driver has been subject to our internal disciplinary process.
He has acknowledged his mistake and has apologised for the incident.
He added that the firm has invested £370m in the last five years on new fully accessible buses and added that they work closely with disability groups on the internal design of their vehicles and other issues to help improve the service further.
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Greater Manchester Police said "inquiries are ongoing to fully understand the circumstances of the incident."
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He served in Margaret Thatcher's Cabinet as Home Secretary in 1989 and was also a former Governor of Bermuda.