And fun – and thrills – is what Monday nights are all about for the friends from Hebden Bridge.

All of them old enough and respectable enough to know better! A group of successful, professional women, average age of 42, who come rain or shine, pound the rugged terrain of the Calder Valley moorland on their mountain bikes. At night. With only a headlamp to guide them on their way.

Night riding, or the "New Black" as its become known in mountain biking circles, isn't for the faint-hearted. When you ride at night, even familiar descents become more treacherous, whilst unfamiliar climbs seem to go on forever.

But whilst most of us are scurrying indoors once night falls, these women are gearing up to play out.

"It's exhilerating to ride at night. And it makes going uphill that much easier - you can't see how steep it is," says Heidi Fletcher, 42 and a law reporter.

Initially she agreed to join Birds on Bikes founder members Kirsty Law and and Penny Sheard for a one-off ride. Her partner is a keen biker so she borrowed his lights and, well, the rest is history.

"There's nothing to beat the thrill of flying down a hill, in the pitch black, with the wind on your face," says Helen Sunderland, a 45 year old PA. She's also, incidentally, the latest casualty and presently taking enforced "time out" whilst recovering from several stitches to a nasty wound on her calf!

And besides, the fear of falling off is often greater than the fall itself, the women all agree. Mandy Halstead, 42, a catering instructor in a male prison, was left in agony with severe bruising to her thighs after a particularly painful fall but it wasn't long before she was back in the saddle. And Penny claims the only time she ever completed a perfect cartwheel was when she went flying over the handlebars straight onto her feet!.

It started as a one-off bike ride and slowly but surely, one by one, the women were hooked.

Helen sums it up: "It's my night off, my night to play out. It's like playing out when you were a little girl."

And this is no group of teenage daredevils but a group of professional women - amongst them a barrister, solicitor, a company director and an educational pyschologist - who live for the thrill of Monday nights to help them cope with their busy and often stressful jobs and lives. Between them they have a dozen or so children ranging in age from one to 18. Their own ages ranging from 37 to 48.

Tonight it's a particularly cold, wet, windy Monday night but that makes no difference to these Birds on Bikes.

They arrive back at base shrieking with laughter and covered in mud (after a mud fight on the moors because they thought they looked too clean for the photoshoot!).