Diesel buses were brought in to replace electric buses in York due to charging infrastructure work being delayed at First’s James Street depot.

Four diesel buses from Leeds were being used out of a fleet of 90 as of February 19.

Problems had arisen due to an issue with the level of power supply required to charge them all overnight.

Northern Powergrid is expected to start work to solve the issue in April at the earliest.

The Leeds buses are all Euro VI models and compliant with York’s ‘Clean Air Zone’ requirements.

Tom Donnelly, operations manager of First York, said: “Due to planning and the excellent efforts across our depot team we maintained services with no inconvenience to journeys.

“The disruption to the power output experienced at our depot has been identified and work is well underway to rectify this.

“We retained one or two of the vehicles brought in last week from nearby depots to support service delivery while the power system stabilised.

“All the buses from other areas have now been returned.

“We appreciate the patience and understanding of customers.”

The council’s transport executive, Cllr Pete Kilbane, said: “It is disappointing that problems with the Northern Powergrid’s electricity supply to the First Depot have resulted in a very small number of diesel buses being used to cover the routes.

“Whilst this is far from ideal we think that residents appreciate that a diesel bus is better than no bus at all.

“We will continue to work with the bus companies to bring stability to the bus network and improve reliability.

“One bus failing to turn up is one too many.”

Former Green Party transport executive, Andy D’Agorne, said: “I understand the problems that First has experienced and appreciate the efforts made to maintain bus services at short notice.

“However it does highlight the need for backup overnight charging arrangements maybe at park and ride sites.”

A Northern Powergrid spokesperson said: “Northern Powergrid is completely supportive of First’s plans to operate a 100 per cent electric bus fleet in York and have brought forward a significant investment in the local electricity network to support this.

“We are currently in the process of carrying out a major investment scheme to create the additional capacity that First needs to operate a 100 per cent electric fleet as quickly as possible, while following the legal processes we must adhere to around securing planning and permissions to work on private land.

“In the meantime, to provide additional interim support, Northern Powergrid has provided a temporary uplift in power which does not support charging of the full electric fleet but will provide a temporary solution to support the operation of a small number of electric buses on a pilot basis, whilst the longer-term project is carried out.

“We will continue to work closely with York City Council and the third-party landowners whose permissions we need to complete the work, to support First York’s plans to run an electric fleet of buses, and we are optimistic this will be possible from the end of April/early May.”