The acute problems suffered by First in Glasgow and central Scotland are also shared by several other firms across Scotland, with West Coast Motors and Borders Buses “just making service with all hands on deck”.
First has been forced to make short-notice cancellations which have reduced the frequency of some services in central Scotland from half-hourly to hourly.
Services on some Glasgow routes are down from 12 to 15-minute frequencies.
First has already been prevented from increasing services from 85 to 90 per cent of its normal timetable.
It is 17 per cent short of the number of drivers it needs to run a full service.
The Confederation of Passenger Transport UK - Scotland (CPT), which represents operators, said vacancies had doubled since 2019 to average 12.5 per cent across Scotland.
First Scotland interim managing director Duncan Cameron said: “We are going to have to reduce the timetable further to improve reliability.
"Things will get worse, but I hope this is the last time we will have to do it.”
He said the shortage had been caused by training being delayed by the Covid lockdowns, long waits for new licences being issued and the “hottest” employment market for 20 years prompting some would-be drivers opting for other jobs instead.
Haulage ‘getting more priority’
Mr Cameron also expressed concern about the Driver and Vehicle Licensing Agency (DVLA) writing to bus drivers to ask them to consider driving lorries.
He said: “The heavy goods vehicles logistics shortage is not the only problem when bus companies cannot run full timetables.
"It seems that sector is receiving much more attention and priority than us.”
Lothian, Edinburgh’s main bus operator, said it was also short of drivers, but services had not been affected so far.
A spokesperson said: “Like many other transport providers, Lothian are in an extremely challenging recruitment market which, coupled with delays to medicals and licence applications, together with our safety protocols for colleagues who find themselves in the Covid-19 track and trace cycle, means we are experiencing resourcing difficulties in our driving team on a day-to-day basis.
Bus firm owner driving
“Fortunately, however, we are better placed than many other operators and we are hopeful that some of the pressures we are currently facing will begin to reduce as the combined impact of these factors begins to lessen.”
Jointly-owned West Coast Motors and Borders Buses said: “We are struggling for drivers like most. However, we are just making service with all hands on deck.
"All those who have a licence, including managers and the owner, are driving.”
Stagecoach declined to give details of how it had been affected, but admitted to short-term changes in some areas.
A spokesperson said it was “continuing to operate the majority of our bus services” and seeking to resume a full timetable “as quickly as possible”, adding: "We are seeing continued strong demand for jobs in our sector and are focused on getting the new drivers who are in our training pipeline on the road as soon as DVLA licensing delays allow.”
CPT UK – Scotland director Paul White said the “vast majority of services” were running normally across the country and operators were prioritising popular routes where there was disruption.