It is not literally an exchange, you'll be relieved to know, but a new twist on an old ruse: the chain letter. Most chain letters promise untold good luck or a fast buck. They circulate at every level, from the third form to the boardroom, playing on our superstitions and rarely delivering what they promise. This chain letter is different: its currency is lingerie and it's for women only. It does, however, still involve burdening your friends, who may roar with laughter, but may equally well groan and curse you.
'Send ONE new pair of pretty underwear of your choice to the first person below and send a copy of this letter to seven friends.' The letter shows two names. Having dispatched a pair of knickers ('a manilla envelope will mail the underwear nicely') to the first person, you strike off her name and address, add your own ('Don't forget to mention your size]]]') and send it on. Your seven friends will each send the letter to seven people, with your name and dimensions topping the bill. Within a few weeks your doormat should be a pile of envelopes.
Philippa Richardson, a 23- year-old market researcher who joined the chain a few weeks ago has received two pairs already: 'One were kinky red sateen, and the others were from Marks & Spencer, and came with a receipt, which I thought was very considerate.'
Women who are taking part say the 'Exchange' works because the idea tickles and because the chain is wide but short. 'There are only two names on the letter, so you've got badgering power,' explains Ms Richardson.
The idea of women sending underwear to complete strangers is quite odd, though, and has two, divergent, effects on the choice. 'I sent off some M&S knickers - nice and lacy and white. They cost pounds 3.50,' says Ms Richardson. Another signatory, Emma Arkell, 26, a law student, says: 'If a man gives you underwear, it's really for himself. Whereas from women you're more likely to get something you'd actually wear - not nasty and black with red ribbons. I wouldn't want to be sent 49 pairs of G-strings.'
But the women-only rule also allows women to give each other titillating saucy underwear, in a giggly, hen-party kind of way, without the connotations of being compromised or exploited. Frieda Pattenden, a 25-year-old teacher, received an underwear chain letter from Australia. 'I sent a pair of crotchless knickers.' Perhaps because of the distance, she never received anything in return. 'Still, I wasn't really doing it for the knickers, but for a joke. My brother's fiancee had started it.'
Tell a man about the chain letter and he will show initial fascination, which turns to boredom on hearing that most of the underwear involved is white, functional and decorous. Women say things like, 'What a brilliant idea. How can I join in?' Only one person really hated the prospect. 'It's so overtly sexual,' she said. 'What if some pervert got hold of the letter?'
This fear is not shared. Those who have joined believe they have nothing worse to lose than the price of a pair of knickers and a few stamps. Claire Davies, 26, a PR account executive, says: 'It's a great idea. I'm doing it for fun . . . and for the 49 pairs.'