Wahaca promises a taste of 'true' Mexico. But how authentic can it get in a posh shopping centre in west London?

This is a first: not only am I eating in a shopping centre, but I am eating Mexican. And I'm sober. Next to me, two big, beefy blokes work their way through enormous burritos and tortilla chips; on the other side, toddlers in highchairs cut their teeth on soft tortillas as mum and dad share enchiladas. None of them appears to be drunk, either. But I thought it was a prerequisite – how else can you down all that stodge, cope with all that chilli, digest all that cheese? And, frankly, why else would you?

The £1.7bn Westfield London at White City has installed a "high street" full of food chains along its Southern Terrace to cope with the demands of its visitors – 9m to date. Meat & Wine Co, Ciao Baby Cucina, Kitchen Italia, Del'Aziz, Gourmet Burger Kitchen, and Wagamama are all present and correct, so the fact that Wahaca, younger sibling of the successful Covent Garden mothership, is also here, suggests the owners are moving from an ethnic foodie niche bracelet to a fully fledged chain.

Launched by slinky former Masterchef winner Thomasina Miers and business partner Mark Selby, Wahaca is designed to introduce "proper" Mexican food to London. It is not alone. A Mexican wave is engulfing the capital, driven by cheeky Chilango, burrito-happy Benito's Hat, and bar-sceney Green & Red, proving there is life beyond Tex-Mex refried beans and greasy nachos.

It is ambitious to hitch noble principles to the cart of a chain in the making, but Wahaca attempts to source ingredients locally (including habanero chillies from Kent and Lancashire cheese for the quesadillas), with commitments made to free-range (pork and chicken), Fairtrade (tea and coffee) and sustainability (Marine Stewardship Council-certified fish).

But let's not get too carried away. We are still talking about Mexican food, and Wahaca isn't stretching it too far upmarket, with its cheese-laden quesadillas, rice-filled burritos and margarita cocktails. Every order starts with a bucket of crisp tortilla chips to dip into a fresh chilli salsa (£2). Even sober, I can handle the pork pibil tacos (£3.75) – three small, soft corn tortillas topped with slow-cooked, shredded pork and pink, lightly pickled onion. In fact, I could handle a few more. A burrito (big fat tortilla-wrapped bundle) of chicken, black beans and green rice (£5.75) tastes only of rice, but is strangely comforting.

While newcomer Chilango does more generous, multicoloured fillings, Wahaca's dusky, softly chewy tortilla wrap is far better, with a real character of its own. Tostadas (£3.50), two crisp mini tortillas generously piled with smoked mackerel, black beans and chipotle mayo, come frigidly cold. Two salsas arrive, the smoky red chipotle adding more interest than the green tomatillo, which is mild-mannered in spite of being described as "searing". The habanero-chilli sauce that sits on every table is definitely searing, on the other hand, and wonderfully so.

Two downers: a glass of citrus fizz (£1.45) has blackened mint leaves and yellowing pre-cut lime wedges; and the grilled fish of the day (bream, £9.95) is a dud, with no apparent relationship to its description.

Even after a Pacifico beer (£3.50) and a good-value glass of fruity, juicy Argento Argentinian Pinot Grigio (£4.25 a glass/ £15.75 a bottle), I'm a long way from drunk, so I am not sure I can judge Mexican food under such a handicap.

Wahaca is halfway there. It should be bolder, fresher, sunnier, juicier, spicier and punchier, with better day-to-day cooking skills. But it isn't bad, given the prices; nor is the food completely deep-fried or buried under cheese. I will consider going back some time when I am out of my tree, so I can give you a more informed opinion.

13/20

Scores: 1-9 stay home and cook, 10-11 needs help, 12 ok, 13 pleasant enough, 14 good, 15 very good, 16 capable of greatness, 17 special, can't wait to go back, 18 highly honourable, 19 unique and memorable, 20 as good as it gets

Wahaca, 1074 Westfield Shopping Centre, Ariel Way, White City, London W12, tel: 020 8749 4517. Open noon-11pm, Monday-Saturday; noon-10pm, Sunday. Around £40 for two, including wine and service

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