Peter Johnson, director of Johnsons Coach and Bus Travel, said: “It is a serious thing for us. We’ve apologised, especially to the parents involved.”

Although the coach went no further than Warwick School after dropping girls off at King’s High, there are concerns that the driver did not stop when he was first asked by the children.

The clutch developed a fault on the hill on Saltisford, and started blowing smoke and fumes into the coach.

Mr Johnson said of the driver: “He did the right thing; he got the kids to the safest place. He probably had a few difficulties realising because he is at the front and the kids are at the back.”

But headteachers may take further action after this week’s half-term break. In a joint statement, Ed Halse, head of Warwick School, and Elizabeth Surber, head of King’s High, said: “We take the health and safety and the welfare of all our pupils very seriously indeed. We were concerned by the incident and the bus company was contacted immediately and parents were also notified. The schools have requested a full investigation by the coach company into the incident and await the report.”

The head of the Kingsley School, Heather Owens, had serious concerns about the incident. “Several girls felt unwell when they arrived at school and were seen by our nurse before being sent home,” she said.