By Emma Griffiths BBC News, London

The concourse is a sun trap. Throngs of tourists head to nearby Madame Tussauds or cram onto open top buses pulling up outside.

Here bright T-shirts, flip flops and summer dresses are the outfits of choice. Where shirts are worn, sleeves are rolled up to the elbows. Most people seem relaxed.

But below the streets, people are hotter under the collar. Five Tube lines pass through Baker Street and those who have to travel at rush hour are feeling the heat.

"Bloody sweltering", was how video editor Rachel Grierson, 26, from Australia, summed up her Tube journey.

Not prepared

"In Brisbane everyone just stays in shopping centres, where there's hardcore air conditioning. It feels hotter here than Australia, because I don't think England is prepared for it."

Rachel Watkins, 20, a student from Chorleywood, Herts, had just arrived back in the UK after a holiday and was lugging a big suitcase back home.

"It's so hot I can't believe it, I was hoping it was going to be nice and cool," she said.

"It was hotter in Corsica, but it was a drier heat and there was a pool to jump into."

Rachel Grierson and Leon Stuparich say it's "sweltering"

Over the years unions have negotiated some relief for Tube drivers, including air conditioned restrooms, facial wipes and soft drinks.

An Aslef spokesman said the Piccadilly Line was the best, but in some cases Peltier cooling units have been installed in driving cabs.

"You are only there for 20 minutes, we are there for eight hours," he pointed out.

But in the passenger section, temperatures keep rising.

London Underground would not comment on reports they hit 47C on the Central Line on Monday. A spokesman said generally they were the same or a few degrees higher than the outside temperature.

If you get stuck on a track it's unbearable Claire Winfield

People have different ways of staying cool. Maysa Mahfonz, 18, uses a hand-held fan, although says it is a bit embarrassing "because everyone is looking". Ms Grierson carries a bottle of water, tries not to stand near anybody else nor move about too much.

Ian Campbell, works in local government, and has to wear a suit to meetings.

"It can be [unbearable] on the Tube, if you are there any length of time. It can be very bad but you can always take your jacket off."

Claire Winfield, 30, a massage therapist from Stanmore, has to get the Tube in during the morning rush hour and in the early afternoon - when the sun streams into carriages of overground services.

A groundwater cooling system is being trialled

"I use mainly the Metropolitan Line on a daily basis. Most of that is overground but if you get stuck on a track it's unbearable, awful and there have been lots of delays recently."

"When it's packed, it's worse, but generally it's like a greenhouse effect, especially at 2pm, when the sun's really strong. Even if the Tube is empty, it's enclosed and there's no air conditioning."

LU has long struggled with the problem of getting heat out of narrow Tube tunnels - some built more than a century ago.

Its most recent project, being carried out at Victoria, involves using a groundwater cooling system to suck in warm air and pump out cool air on platforms of deep-level stations.

'I'd rather walk'

But mayor Ken Livingstone has warned that if temperatures keep rising, in future parts of the Tube may have to shut to save lives.

One Evening Standard seller was enjoying a cooler spot at the foot of the stairs, out of the sunlight. He gets an air-conditioned train to nearby Marylebone. But he said he gets a good view of commuters coming off the Tube trains.

"They were really looking rough last night, there were big time delays because of the hot weather and all that."

He nods at the trains and adds: "I'd rather take a walk than sit on one of them."