Ticket machine glitches have meant bus passengers have been wrongly travelling for free.
The national Concessionary Bus Fare scheme means that pensioners and the disabled get free travel anywhere in England from 9.30am to 11pm Monday to Friday.
However, to allow its vulnerable residents to continue travelling without charge on night buses within the city, Brighton and Hove City Council provides extra cash to extend the benefit into the early hours.
Yet Brighton and Hove Bus Company has confirmed its automatic ticket readers, which were first installed on its fleet in June, cannot distinguish between a concessionary card issued in the city and one from outside.
Fuss This means that tourists and those living in areas just outside Brighton and Hove, such as Shoreham, Peacehaven and Worthing, have been travelling for free outside the national restrictions.
Roger French, managing director of Brighton and Hove Bus Company, said: “Since Monday the checking of passes has been done manually so drivers can differentiate between them.
“It’s how they used to do it before the machines came in so it’s not a problem.
“We’re talking penny numbers of passengers to be honest.
“The chances of people outside the area using the night buses, which mostly run within the city, are very very small.”
The national concessionary bus scheme gives free travel to those aged over 65 and the disabled.
There are no time restrictions for any passes at weekends and on Bank Holidays.
However, local authorities have the option of using its own money to extend the weekday restrictions.
In Brighton and Hove, the council pays for its own residents to get free bus travel from 9am every day.
They can also board with no charge from 11pm to 4am Monday to Friday.
Pass holders who do not live in the city are expected to pay if they travel outside the national times.
Bus drivers were told of the changes to the scheme on Monday.
However, some thought it meant it affected all concessionary card holders, not just those issued outside Brighton and Hove.
One driver, who did not want to be named, said: “It caused quite a bit of fuss from the sounds of things as people who thought they could get on for free were told to pay for their fares.”
Any loss of revenue will affect the bus company as it has signed a three year fixed price deal with the city council.
Mr French said: “Financially we have been missing out but I’m guessing we’re talking about one or two people every month. We need to get it sorted.”