Passengers were left to swelter in unbearable temperatures on board a Bristol bus on the hottest day of the year when the driver was unable to stop heat from the engine spreading to the rest of the bus.

Fishponds man Patrick Steer is disgusted that the design of buses by company First, means that it is only an engineer, not the driver, who is able to adjust the bus' temperature.

First insist that the heating in the bus was not switched on but in very hot weather, heat from the engine can pass into a water pipe which runs around the vehicle as part of its engine cooling system.

Mr Steer said elderly people could die of heat stroke if First fails to sort out the problem.

The 58-year-old takes the 29-minute journey on the number six bus to and from his work in Wine Street, Bristol, every week day.

But on Monday, when temperatures in the city reached 28°C, passengers on the bus had to endure additional heat on their journeys home.

The administrative officer for JobCentre Plus said he complained to First when he noticed the heating had been left on a week ago, but claims that nothing has been done to rectify the situation.

He told the Bristol Evening Post: "First told me that the driver has no control over the heating and that it is down to the engineers to change the temperature.

"Where I work I sit by the window with the blinds down and my fan switched on. I go the entire day without breaking sweat, until I get on the bus. It was just appalling.

"I had my jacket and tie off. This journey made me break sweat for the first time that I can remember. In this climate, if we don't go down the American route of having air-con, the least bus companies should do is turn off the heating. In a car the driver can control the temperature, so why can't the bus driver?"

Mr Steer, who lives in Mayfield Park with his partner and has grown-up children, said everyone on the bus on Monday afternoon was distressed.

He added: "I'm an averagely healthy man for my age and I'm a skinny fellow. But if I was 10 years older and a bit tubby I would have expired on that bus. Everyone was uncomfortable on that journey.

"People were waving fans in their face, I didn't see anyone who wasn't sweating. I was quite distressed. My mum died a year ago, but if she had been on that bus I don't think she would have survived the trip."

First spokeswoman Suzannah Marsh said: "The heating is currently switched off on all our buses, however operating in this very warm weather means that heat from the engine can sometimes present a challenge.

"We are sorry if this customer experienced discomfort and are ensuring his complaint is looked into.

"We are making significant investment in our fleet. For example we have just introduced 16 brand new buses on routes 48/49 as part of our £20 million investment in the Greater Bristol Bus Network."