'IF you're any bigger than a 32D, don't try this," advises Kate Humble as she squeezes herself, and I really mean squeezes, through an impossibly small gap in the rocks. There's worse to come as she follows fellow BBC presenters Kate Silverton and Julia Bradbury in being scared as she undertakes an extreme sport.

Their challenges - climbing mountains and navigating wild water - seem easy-peasy compared to the tight spots in which Humble, best known for assisting Bill Oddie in Springwatch and its seasonal variations, finds herself.

The long crawl comes underground in South Wales. The tight and narrow tunnel is "the ultimate squeeze" that involves crawling the length of a football pitch in a passage not wider than a car tyre. I shared her companion Steve Backshall's panic as he got halfway along the crawl, that lasts more than an hour, and realised that essentially he was buried alive.

TV proves an ideal medium for conveying the dark, dank, claustrophobic world of caving. I felt terrified and I was sitting in the comfort of my home in a light and airy room, wondering why Humble had subjected herself to this ordeal. How much nicer to be sitting next to Oddie watching badgers come out to play at night time.

Instead, she opts to go to "a place where few dare enter" in the words of the narrator, a real scaremonger who notes that "her life could be in danger as she descends into the depths of the British underworld". It makes her sound like she's off to become a gangster's moll.

Caving experts Tim and Pam set her four challenges, each offering distinct and increasingly difficult tasks. Of course, she sheds a few tears (reducing a strong woman to sobbing is a requirement of these Ultimate shows) and says exactly what you're thinking, such as "you must be joking" on seeing the first tunnel through which she must crawl.

Happily, she doesn't lose her footing - caving involves as much climbing as crawling - or sense of humour. Emerging after a day underground, she's dying for a wee but hampered by an inability to undo the buckles and belts of her caving gear. Eventually, she manages and the camera shows her running off into the countryside in search of a convenient bush. "You've still got your microphone on," someone shouts after her.

"You'll just have to listen," she screams back, knowing that when you gotta go, you gotta go even if half the nation can hear you peeing.

Like Humble, writer Graham Linehan shows considerable nerve with the returning comedy The IT Crowd - by cramming as many gay gags in 30 minutes as he can. The plot revolves around whether Philip is gay. He reads Heat magazine and knows people in the theatre which marks him out as that way inclined in the minds of Roy (Chris O'Down) and Moss (Richard Ayoade). Their view is reinforced when he invites Jen (Katharine Parkinson) to see a stage musical called Gay!

Having run out of gay jokes, the script moves on to disabled people, with tipping a man out of a wheelchair and other gags. At least, Philip comes out of the closet, telling Jen: "I thought I could make it work between us because you look a bit like a man".