PROBLEMS with South West Trains' air conditioning during the recent heatwave have left many passengers hot under the collar.

Britain's biggest train company has admitted that a number of trains experienced problems over the past few weeks as temperatures topped 28 Celsius.

But the firm has also blamed hot, sweaty passengers getting off the tube and on to trains heading for Hampshire for adding to a sticky situation.

The rail operator claims many of its train's mechanical systems cannot cope with such warm temperatures and malfunction leaving hundreds of passengers stifling in sauna-like conditions.

It has been reported that onboard cafs have been doing a roaring trade with passengers queuing for refreshing drinks on services from London Waterloo.

A spokeswoman for South West Trains, which makes a £1m profit a week, said there was a problem on their older Wessex Electric Trains but also on the brand new state-of-the-art Desiro models.

"We were aware of the problems on the Wessex Electric's and have been working to refurbish them," she said.

"Our Desiro trains are very modern and computerised and as soon as the temperature gets too high the computer detects an error and shuts down.

"It is extremely difficult to keep what is essentially a long metal tube cool when the temperature outside is approaching 30 Celsius."

She added that the large number of hot passengers being carried also increased the onboard temperature.

"We don't know if onboard shop sales have gone up but if it is hot we assume people are buying more," she said.

"We do apologise to passengers who travel on these defective trains but the majority work fine and we are trying to sort the remainder out."

Tim Nicholson, chairman of the Rail Passengers Committee for Southern England, said every season brought a different problem for rail operators.

"There could be leaves on the track, the wrong kind of snow, warping of the rails in the heat or faulty air conditioning.

"Passengers don't want these excuses, they want the problems solved," he said. "South West needs to increase the reliability and functionality of its trains. They also need to upgrade the systems to stand the extremes of heat we are now experiencing and stop blaming passengers."

German-built Desiro trains have been phased in to replace the old slam door trains and are said to be the most technically advanced trains in Britain.