City Life: Mexico City - Authentic Mexican food: Worms and flies' eggs down Mexico way at the heart all Sweet living on a diet of lightly fried worms

CARLOS AND Concha are determined to educate my palate. They always mock the Mexican food I used to feast on in London - mostly corn chips, bean dip and salsa - as bastardised Tex-Mex concoctions. They also avoid the overrated fusion restaurants that line the touristy Zona Rosa in Mexico City: these borrow freely from Californian or Mediterranean fads and are too heavy on the goat's cheese and sundried tomatoes. My gourmet friends prefer pre- conquest recipes with unpronounceable Nahuatl names.

They even turn up their noses at the wheat tortillas so typical of north Mexican cooking, because they claim wheat only arrived in MesoAmerica when the Spanish missionaries needed dough to bake their Eucharist wafers. "Inquisition fodder," Carlos sneers. "Corn tortillas taste so much better." Ethnic chic definitely will be on the menu today.

Fine dining in Mexico usually occurs in the middle of the afternoon, between 2.30 and 5.00pm, when work halts and everyone tucks into the main meal. Spreading a crisp white linen napkin over my lap, I agree to let my two mentors do all the ordering, and am quite amused at how they grill the waiter to make sure each item is at the height of its season.

Crepes made from huitlacoche, a tasty fungus that grows on corn ears, do not faze me. The flavour is slightly smokey with a spicy aftertang and the concept a bit like roquefort cheese. But when I overhear Concha request Maggi sauce, I am taken aback.

Not Maggi, she assures me, but maguey. This is the spiky century plant that thrives in Mexico's most arid places and shoots up a towering stalk of creamy flowers every decade or so. Only long-nosed bats can pollinate it. Tequila is distilled from blue maguey plants, Carlos instructs me, and fermented maguey sap rated its own Aztec divinity. Two thousand years ago, it was a valued intoxicant for priests and sacrificial victims alike, and drinking it is guaranteed to whet the appetite. So far, I am intrigued.

But it turns out that our order is not for mezcal liquor or even pulque, a less refined drink made from the maguey plant. With a flourish, the gloved waiter presents our entree: gusanos de maguey. I try not to show my shock. It is a platter of freshly sauted maguey worms, dusted with cayenne pepper.

These are just like the single ghostly larva, curled at the bottom of a mezcal bottle, which the losers used to gobble down with their eyes closed at the end of my most decadent college drinking sessions. Only now there are lots - and this is lunch. Glancing around the restaurant, it is clear that this summer delicacy is in demand and my friends are not pulling some nasty culinary prank on the "gringo" Apparently epicures look forward all year to the rainy season when it is peak time for gusanos.

This is Mexican grub, all right. Concha notices my hesitation and clasps my fork-wielding hand.

"Listen, I used to think prawns were disgusting, with all those legs and antennae, until I finally tasted one," she cajoles. "Go ahead. These gusanos are food fit for emperors. You find them at the heart of the maguey, drinking the divine nectar." Squeamishly, I bite down into one. Most people say any exotic meat tastes vaguely like chicken. Well, not these worms - although the taste comes pretty close to fried calamari.

As I chew more thoroughly, it grows weirdly sweet and the texture seems a bit wobblier than squid.

"It's not actually a worm, more like a caterpillar," Carlos says in an attempt to boost their appeal. "Some people say gusanos are an aphrodisiac because they are loaded with vitamin E. Plenty of iron, too, plus vitamins A and C. Think of it as health food."

A shot of tequila helps considerably, and I douse the next helping of worms with fiery chilly chunks, more to hide the appearance than mask the taste. I wonder if the red variety look more appetising than these fat white grubs.

Despite Carlos's urging, I forego the ahuatli, "Mexican caviar" made from flies' eggs. Ditto the transparent ezcahuitl larvae which eventually turn into tiny ants. Already, I had congratulated myself for my diner's daring when I wolfed down beef brain burritos at Carlos's barbecue last week without worrying unduly about mad cow disease. If I did not draw the line somewhere, Concha would have me chewing down on iguana or dog tamales in the name of tradition.

A recent study showed Britain taking to Mexican cuisine with a vengeance. According to Louis Barf, of Key Note market research, Mexican fare ranks just beneath Indian and Chinese in British sales. But we have still got a lot to learn about what is cooking.

There was a run on jalapeno peppers and chipotle chillies at the second British Ethnic Food Show in June. Not so for the mole sauce - even though it has nothing to do with the garden variety rodents which make molehills. Mole rhymes with ole, and is Mexico's national dish made from chocolate, cinnamon, spices and chilly. If this aromatic dish put the punters off, I doubt that many went for the gusanos de maguey.