TO some they're sexy and to others they're just plain uncomfortable. But whatever you think of them, there's no denying that G-strings are more popular than they've ever been.

Underwear industry experts say G-strings, or thongs, are now so widely worn that sales match those of traditional, often more comfortable, knickers.

They began to get more popular about five years ago, championed by women who were trying to get rid of a visible panty line (VPL) when wearing tight-fitting clothes.

But since then their appeal has broadened, and they are now seen by many women as everyday underwear.

The fact that stars such as Jennifer Aniston and Britney Spears have been seen wearing G-strings under their low-slung trousers have done nothing to dent the popularity of the underwear, although whether Victoria Beckham's cheeky admission that her husband David has been known to wear her thongs has done anything for their image is open to debate.

But one issue open to debate is the reason behind their increasing popularity. Is it because they're actually comfier than they look, is it just that women buy them because their friends have them, or does it simply boil down to sex appeal?

Pamela Scott, editor of the underwear industry magazine Underlines, believes it's not because they're comfortable. It's because they're sexy.

"It boils down to sex appeal -- it has to," she says.

"There's a sexual decision behind it, whether it's conscious or unconscious. After all, G-strings aren't the most comfortable pants on the market."

They might not be comfortable, but Scott says they are now nearly rivalling traditional bigger knickers on the popularity front.

"I've been in this business for 20 years and I can tell you the G-string has never been more popular. There is now one G-string for every normal pair of pants."

There's no doubt that G-strings have come a long way from the early days when they were worn to avoid a VPL.

Now, says Scott, it's trendy to flash your G-string above your low-slung trousers, just like many celebrities do.

"It's come full-circle," she says. "Some women are wearing them so they can be seen at the back. It's no accident that you see them, and this is why some G-strings have designs on the back. It's a fashion statement."

It may be a fashion statement for people like Posh Spice, who flashes her thong as she bends down to kiss her son, but there are definitely a lot of women who would rather keep their G-strings to themselves.

That's why casualwear retailer Republic is about to launch a campaign against VPH -- Visible Pant Horror.

The company is sending Pants Police to its stores, armed with a pocket-sized Pant-o-Meter designed to measure the amount of pants rising above trouser level.

Suzanne Flanagan, Republic's marketing manager, says: "You can measure the level of your shame with the Pant-o-Meter. Lots of celebrities are revealing their G-strings when they're doing things like getting out of a taxi -- it's a big thing.

"But we're doing our best to help avoid visible pant horror by giving away a low-slung G-string with every pair of women's jeans we sell. Then women will be able to keep their pants to themselves."

But the women who don't always want to keep their G-strings to themselves there are even paper G-strings, designed to be thrown away after use. The One For The Road pants are sold by the fashion chain H&M, which says they are "a fun thing."

If the paper option doesn't grab you, there are still alternative G-strings, including bigger sized thongs and even control strings.

High street chain Marks and Spencer, which sells more underwear in the UK than any other retailer, says it has seen an increase in G-string sales.

According to the store: "G-strings are very popular and have been for a while."

But there the company doesn't believe it's the end for traditional knickers just yet.

For G-strings with a twist, the store's Shapewear control underwear, for bigger women who still want sexy knickers, includes strings and lace in its range.

Shapewear focuses on different areas of the body and concentrates on sculpting it in an effort to succeed where diet and exercise may have failed. It does so with pants and other underwear that flatten the tummy, lift the bottom and shape the hips and thighs.

Pamela Scott, of Underlines magazine, says the control, or shapers, ranges on the market have a loyal following.

"They are a steady part of the market," she says. "But there's not the demand for them like there is for G-strings.

"But if they're making thongs with control panels on the front then that might attract the women who don't like admitting to wearing them. That will make them a bit more socially acceptable, but I don't know whether you could ever call control sexy, even if it is in a G-string."