The firm said it was already facing challenges filling driver roles prior to recent operational changes, which saw the closure of its Redcar depot.

Arriva North East has said sorry to passengers for disruption to Teesside and East Cleveland bus services and cited driver shortages as the main cause.

Redcar and Cleveland Council leader Alec Brown claimed he had received a ten-fold increase in complaints from residents over the past few weeks about unreliable buses.

Councillor Brown blamed matters on the closure last month of Arriva’s depot in Dormanstown, Redcar, which has seen staff moved to another depot in Stockton.

Some drivers are understood to have left the company in the wake of the restructuring, having declined to transfer over.

One of the worst affected services has been the 63 which operates from Middlesbrough bus station to Redcar, but others have also been hit.

An Arriva North East spokesperson said: “We know some services in Redcar, East Cleveland and the wider Tees Valley area haven’t been as reliable as customers expect in recent weeks, and we’re sorry for the disruption this has caused.”

It conceded the overriding factor was “driver availability” and it was taking steps to address the problem, and expected “reliability to strengthen”.

Writing on Facebook, Coun Brown said he had previously relayed “serious concerns” to Arriva North East, including in a meeting with its chief executive, but was reassured there would be no impact from the changes.

He said: “Arriva closing its Redcar depot and office is already having a real impact on passengers across our borough.

“Over the last few weeks, I have seen a tenfold increase in complaints about bus routes, reliability, cancellations and the general service people are receiving.”

Coun Brown said passengers “need answers about what is happening” and for many people “buses aren’t a luxury”.

He said:“They are how they get to work, school, college, hospital appointments, the shops and to see family and friends.

“When services are unreliable or disappear altogether, it can have a huge impact on people’s lives.”

Speaking to the Local Democracy Reporting Service (LDRS), Coun Brown said: “The Redcar depot closed about two weeks ago and since then cancellations have gone through the roof.

“I have been told by other drivers that they are trying to get emergency staff in.

“This was all very predictable.

“People have been stranded, old people are missing medical appointments, some people are choosing to stay in because they are not convinced they are going to get home.”

Coun Brown said the council had interviewed a few of the affected drivers who had applied for posts with the local authority and taken some on.

He also said he and local MPs Anna Turley and Luke Myer had sent a joint letter to the regional Traffic Commissioner, which licenses bus and coach operators and oversees the registration of their routes, expressing concern at events.

Another councillor, Barry Hunt, who represents Brotton ward in Redcar and Cleveland, told the LDRS that Arriva were a “law unto themselves”.

He described the current situation as “sad”, adding; “There are people wanting to get to work from our way and they are just left waiting for a bus.”

Bev King, of the group Friends of Normanby Village, wrote on Facebook that passengers were frustrated and the “impact was visible at Middlesbrough bus station on a daily basis”.

The Arriva North East spokesperson said driver availability was “alreadya challenge across the area before recent operational changes and it has become more visible while staff transition to new arrangements and build up route knowledge”.

They said: “A small number of drivers have chosen to leave the business, but this is not the main cause, it’s added to a challenge we already had plans in place to address.

“There is no vehicle or wider operational issue behind this and there’s been no decision to reduce or change the services we operate.

“Our commitment to the service we provide in the area is unchanged.

“We’re taking a number of steps to improve reliability: drivers from other regions have already joined the North East team to help with key routes, our training schools are running at full capacity and we’ve temporarily moved a small number of services to nearby depots to ease pressure in the short term.

“We’ve made a multi-million-pound investment in 34 new vehicles, specifically targeted to operate within the Redcar and East Cleveland area, and they’re entering service between now and Christmas.

“We’re already seeing an improving trend and expect reliability to strengthen.”