Schoolchildren feared they might have suffered carbon monoxide poisoning after their school bus filled with black smoke.

Fifteen-year-old Mark Britton was one of about 70 pupils from King Alfred's School in Wantage who travelled home on Monday afternoon on the double-decker bus.

The pupils said smoke billowed up from the seats in the lower deck of the bus, which belongs to the School Bus and Coach Company based in Kingston Bagpuize.

The firm said it had the bus checked over afterwards, and no problems were detected.

The teenager, who lives in East Hendred, told the Oxford Mail that when pupils alerted the driver to the problem, he continued driving, jokingly telling them to hold their breath.

He said: "There was black smoke coming up through the seats. When we were still in Wantage, it was OK. No-one was feeling ill. But then a few of us started getting headaches. I opened the windows to try to get some fresh air in. We thought it could be carbon monoxide and were afraid of being poisoned.

"My head and nose started aching and before long, my head was killing me. Then once I'd got off the bus and was nearly home, my nose just started pouring with blood."

Another 15-year-old pupil, who did not want to be named, said: "We were shouting at the driver telling him there was smoke but he just ignored us.

"I started feeling really dizzy and sick and my head hurt. I thought I was going to faint. Lots of us had these symptoms."

Mark's father, Martin, 46, said: "I couldn't believe it when I saw Mark come in from school. He staggered up the drive and had blood down his shirt where his nose was bleeding. I immediately thought he'd been in a fight.

"He said another girl had almost passed out she'd become so dizzy and others had been feeling sick.

"I phoned the police to tell them what he'd told me and they said to get him to hospital to be checked over.

"There were kids as young as 11 on that bus who could have been seriously hurt."

But last night Peter Skinner, managing director of the School Bus and Coach Company, told the Oxford Mail that two of the company's engineers had examined the vehicle and taken it on an extended road test, during which no fumes had been detected.

Mr Skinner said the bus was yesterday taken to the Vehicle Inspectorate in Newbury where it was thoroughly checked and given a clean bill of health. It had passed its MoT on September 19.