James Easdale – whose company Dalglen (No 1813) Limited donated £150,000 to Scottish Labour – added: “There is also a fundamental question about fairness and transparency in how this funding has been allocated.

“We have looked very closely at the scoring process and reached the inevitable conclusion that a legal appeal had to be submitted.”

McGill’s previously secured £8.66m in government support for 41 buses through the first phase of the scheme in 2022.

The firm was also part of a consortium led by energy technology company Zenobe, which was awarded £41.7m, for 42 buses in the second phase of ScotZeb in 2024.

A Transport Scotland spokesman said: “We are aware that McGill’s Buses has submitted a claim to the Competition Appeal Tribunal.

“As this matter relates to legal proceedings, it would not be appropriate to comment further at this stage.”