'In theory," says language teacher Paul Noble, forming a steeple with his fingers in true professorial style, "you should learn Chinese today and tomorrow quicker than anyone has ever learned it on the planet." In theory, because I'm the very first student to take his intensive two-day course in Mandarin, which he is teaching me with his wife, native speaker Kai-Ti Chou, in the basement of a north London art gallery. If their prototype course works as well as they are hoping, then two days from now I will, as the spiel on Noble's website boasts, "have learned to speak Chinese the way it is really spoken".

It's a bold claim. Mandarin has a reputation as one of the hardest languages to learn. For one thing, it is tonal – each word has a variety of possible meanings, all dependent on the subtlest differences of pronunciation. A downwards, chastising inflection converts the word for "buy" into "sell", while the incredulous falling and rising third tone transforms the word for "mother" into "horse", and the same word, "ma", used for horses and mothers, is appended to statements to transform them into questions, like a spoken piece of punctuation.

The idea that any language, let alone one so notoriously difficult, can be taught in just two days struck me first as laughable and later, when I realised that I would be the guinea pig, terrifying. I approached the first class expecting to find myself face-to-face with the language-learning world's answer to Sue Sylvester from Glee, a megaphone-wielding, militaristic maniac forcing Chinese words into my head by rote until I curled up in a foetal position, wept blood and begged to go home.

What I did not expect was a warm, soft-spoken man with a bright blond beard who reminded me less of a barking linguistic drill sergeant than a youthful Gandalf the wizard. Noble's teaching, it turns out, is entirely the opposite of the brain-straining I had envisaged. "The important thing is to forget everything and make mistakes," he explains. "I don't want you to try to remember what I teach you. In fact, I want you to forget it." This is going to be easy, I tell myself. Easy and, since I am going to forget it all, useless.

My plan is to test Noble's teaching, when we're done, in conversation with native speakers. I have booked a table at a Mandarin-speaking restaurant in London's Chinatown, where I'm hoping that my authentic Chinese accent will dazzle waiters and fellow diners alike. Ideally, an astonished waiter will ask: "How long have you been learning Chinese?" and I'll reply, nonchalantly: "Oh, you know, just a couple of days, for a laugh." In Mandarin, of course.

The lessons

Noble's method, it turns out, is Socratic and simple, a variation of what's called the Lexical approach, which teaches language not as long lists of words but as a relatively small selection of set phrases – chunks of language that convey implicitly the rules of grammar and sentence structure. He teaches a handful of words and phrases to use as building blocks – I want, she wants, you want a sandwich – and we add prepositions, rules and verbs one by one.

Pronunciation I learn from Kai-Ti, who repeats each sentence I say back to me, slowly and subtly correcting my often inventive pronunciation. Just as the chunked approach taught structure and grammar without making them explicit, by copying Kai-Ti I learn to use the four tones organically.

Day one begins in the present tense, progresses to questions and then on to the past and future. By day two I am playing fast and loose with pronouns, possessives and conditionals, albeit with a very limited vocabulary. I can't help but see the process as a montage scene from a film, a time-lapsed conversation between master and pupil growing rapidly weirder and more complicated:

"I want to go to Beijing."

"Do you want to go Beijing?"

"I want to go to Beijing but you want to go to Shanghai."

"Do you want to go to Shanghai because your mum went to Shanghai?"

"I will go to Beijing because I don't like your mum."

"If you want to go to Shanghai I will go to Beijing and buy your mum."

The narrow set of nouns and verbs is an integral part of Noble's technique. "One of the worst things you can do with language teaching is teach someone a massive number of words. It's back-to-front – teach them to speak and then add to their knowledge. You have to become very fluent in a very small amount of the language." Many students, he says, are led astray by learning numbers, colours or days of the week before they've learned any kind of framework with which to use them. "The nouns are almost irrelevant. That's stuff you can learn yourself."

Though his approach emphasises relaxation and experimentation, there are rules. Writing anything down is banned, as is all technical jargon – talk of participles, perfect tenses and the subjunctive makes Noble wince. "The mistake with language learning is that it's seen as an academic subject, but it isn't; it's a practical subject. What you need is to be trained in them."

He laments the state of language teaching in schools. "I was naturally particularly good at languages but when I went to school they did German and I was utterly confused by it. I spent about eight years trying to learn and failed." It was only after leaving school and experimenting with commercially available language courses that he hit upon methods that worked for him and, he hoped, would work equally well for others.

Though Collins has now published his courses for the public in French, Spanish and Italian, Noble's goal remains to change the way languages are taught in British secondary schools. "If I had four years with kids in schools they would walk out fluent. Instead, I have 10 hours in a classroom on a weekend."

After a hushed discussion in Mandarin, Paul and Kai-Ti give me one last crash course in preparation for my trip to the restaurant. They have chosen what I should order in advance, outlining a selection of standard dishes: Singapore chow mein (Shin-ja-poor chow me-en), Yang Zhou fried rice (Yan-Jo chow fan), Peking duck (Bei-jing kao ya) and, at my request, a glass of orange juice (Ju-tze shui). They teach me how to ask for the bill, how to ask the waiters whether or not they speak Mandarin (as opposed to Cantonese), and how to respond, when asked about the food, that it is tasty or, if the occasion warrants, delicious.

I will not, Noble warns me, understand precisely what the waiting staff are saying to me. "You cannot translate the words as they're being said. It's impossible. You just have to get a general sense." He returns to his notion of language learning as not academic but practical – less a quiz to be answered carefully than an assault course, to be fumbled through at speed. "It's like using the force," he tells me. "Don't try and understand; try and feel."

The restaurant

Six days later I am loitering nervously in the New World restaurant in London's Chinatown, its black-and-red exterior a willing embrace of stereotype, adorned with twin gold dragons and a pagoda-style roof of corrugated tiles. With the notable exception of China itself, it doesn't get more Chinese than this. I have spoken to the staff in advance – in English – and been assigned a Mandarin-speaking waitress, who agrees to indulge me while I road test my two days' knowledge of the language. As I wait to be served I mutter to myself in Chinese, and, to my surprise, it's all coming back to me.

"Ni hao," she says, as she approaches. It's the standard Chinese greeting, which Noble tells me translates approximately as "Y'allright?". He suggests I use "hao" – the equivalent of "fine" – as a sort of catch-all response to any questions I don't understand, as it can mean yes, no, OK, good, bad, whatever.

"Hao," I respond. She asks for my order. This is the part I've been practising longest, and I reel off my intended menu from memory, even managing to improvise successfully around the photographer's last-minute request for a can of Coke. Coca-Cola (in Mandarin, Ke-kou Ke-le) is a word taught early on in Noble's course, as a demonstration that the student already understands at least a little Chinese. She repeats the order in English so I can check that I've said what I meant. It's correct. "Hao," I say. "You speak very well," she tells me. "Sheh sheh," I respond: thanks. So far, so good, but then again, so on script. Ten minutes later, when she returns with the food, I resolve to move the conversation into bolder territory.

"Do you like him?" I ask, indicating the photographer. She laughs, then looks confused and a little panicked. I replay what I've just said in my head. What I've actually asked, I realise, isn't, "Do you like him?" but "Would you like him?" A mistake which is definitely entirely my fault. "Not would you like," I correct myself, "Do you like?" Which, while it is fairly simple, is not a phrase I'd thought about in advance, or constructed in the lesson at all. It's a sentence I've made up on the fly, suggesting that I have, against the odds, achieved some tiny degree of fluency.

There are obvious deficiencies in what I have learned. Chief among them the fact that I know so few nouns; not even, for example, numbers, or months, or farmyard animals, which school language classes had conditioned me to think of as essential. I can, however, convert a verb into the past and future tenses, and say that I, you, we, they, he or she did it, and add an if, a but or a because, and offer, when the situation demands, to buy a stranger's mother or sell them a photographer. Which is more than I ever managed in five years of French at school. Have I really learned Mandarin in just two days? Well, yes and no. Mostly no, but sort of. Hao.

For details of the Paul Noble Language Institute, visit paulnoblelanguages.com. Collins French, Spanish and Italian with Paul Noble are available from collinslanguage.com/paulnoble