I'd done my best - or thought I had - but my best was not good enough.

My girlfriend of the time and I were left rather grazed by the experience (her body, my ego).

My mistake was as elementary as they get.

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I'd been to a boozy Christmas lunch and emerged from the restaurant, squinting into the winter sunshine, with a bright idea in my head.

Why don't I buy some lingerie for my girlfriend? After all, every woman loves beautiful underwear - and every man loves seeing his woman in it.

What a perfect present! What could possibly go wrong?

I'll tell you what could go wrong. I was in London's Soho.

A few tottering steps from the restaurant was a not-so-classy lingerie shop.

Fuelled by the wine I'd downed at lunch, I strode in.

Five minutes later, I emerged with a jet-black bra-and-knicker set made from the world's nastiest nylon and trimmed with the world's scratchiest lace.

You can guess the rest. When my girlfriend of the time - not, I should add, the woman who went on to become my wife - tried on her new outfit, she was unimpressed.

If you want to remove the top layer of your skin, apparently you can buy exfoliating lotions that will do the job for you.

That's not what lingerie is for. She never wore the outfit again.

I learned a simple lesson: leave ladies' underwear to the ladies.

If they want to wear it, they can buy it for themselves.

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This may not be very romantic, but there was nothing much very romantic about me buying cheap, scratchy knickers.

So why do I now find myself in the lingerie section of an Oxford Street department store surrounded by 5,000 bras and knickers?

Because a decade on, I think it's time for another Brief Encounter. And this time, I'm going to get it right.

I'm not doing it on my own.

I am the first student at a Christmas "lingerie academy" for men run by John Lewis.

The store has set up the academy for blokes like me, who like the idea of buying a sexy little outfit for our wives or girlfriends, but who know that, in practice, we can't be trusted to do it properly.

Students will be offered one-to- one guidance by a female sales assistant.

To make the chaps feel at home, the lingerie department will have a comfy sofa, plasma screen TVs, computer games and a fridge full of cold beer.

I've been given a preview before the academy opens next Thursday.

If I'm going to have my fear of ladies' knickers expunged, this is the way to do it.

What could be less threatening than learning about lingerie in the place where I bought my dishwasher and my baby's buggy?

Lead tutor Maria Walker, 38, is John Lewis's chief lingerie fitter.

I've been worried about her since I've known I will be going on this course.

I've heard from friends how some lingerie saleswomen do more than sell their items, they model them - at Agent Provocateur, the saleswomen wear a low-plunging dress that, according to the company's boastful publicity material, "affords a sneaky peep of a sexy bra or a flash of a stocking top and suspender strap".

Well, it's not like that with Maria.

Though she won't like me saying it, her John Lewis uniform, a crisp white buttoned-up blouse and long black baggy trousers, has the look and feel of a dental hygienist.

"We all wear the same uniform," Maria tells me breezily, "whether we're selling washing machines or thongs."

Maria is an attractive woman, warm and witty and exquisitely made up, but there's nothing stridently sexual about her outfit or her demeanour.

She's been selling underwear for 13 years and is a mother of three.

All of this might be a disappointment to a certain type of man, but to this one today, it's only good news.

She tries to put me at ease.

However clueless I feel, there are others worse off than me. "I had a guy once who picked up a suspender belt thinking it was a bra.

"He held it up to his chest and said: "How does she wear that then? Where do these bits go?" When I told him what it was, he asked: "What's that for?"'

I hope you didn't laugh at him, I say.

She pauses just a fraction too long for my liking.

"Er - I laughed with him."

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(The men she appears least impressed with are those who buy two sets of lingerie - one for their wife and one for their mistress.)

I tell her about my previous unhappy experience.

"You made the mistake most men do - you bought for yourself rather than for your girlfriend," she tells me.

Most blokes go for shiny satins in unsubtle reds and stark, unbroken blacks - or, worse than that, a combination of the two.

The worst culprits turn up with a mate.

"It's like Noah's Ark - they come in two-by-two for moral support and gee each other up.

"But they are not thinking about what their wives want. It's all about them."

For a start, she says, their wives may well want lingerie they can wear in the daytime - not just in the bedroom.

Maria takes me over to the back wall of her department.

This is, I soon realise, her least favourite spot in the whole store.

All around are deep red thongs and shiny black bras.

I spot a suspender belt - one of only two that Maria sells.

This is how I imagined lingerie departments to be.

It is, if I'm honest, all rather tarty.

"This is where the men who have no idea head to," she says.

Few women aim for these hangers - except perhaps to return an unwanted gift.

"There are," says Maria delicately, "nicer things you could be buying."

We've been chatting for some time, yet neither of us has mentioned the word bubbling under the surface but never explicitly acknowledged: sex.

In a place like this, it is at once everywhere but nowhere.

For men, it can be difficult to achieve a balance between saucy and sexy, and tawdry and tacky.

My friend Brett - a much more accomplished lingerie buyer than me - claims that there's only one rule in underwear: "as little material as possible".

Maria does not agree with him. Less is not more.

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"My husband says that sometimes the more covered up a woman is, the sexier she is.

"You can unveil things as you go along: you don't want it all out on show."

Brett has another slice of wisdom (rather more reliable, I think): "You can't tell how good a cake will taste by looking at the ingredients on the supermarket shelf."

In other words, how will the pieces of limp material dangling off the hangers look when they're draped over the body of your loved one?

It's damn near impossible to tell. Hence the academy.

But aren't men shy about asking advice about their sex life?

"Men know that we know what it's for," admits Maria.

"I'm like the third person in the bedroom - because I'm advising people on what their wife or girlfriend should be wearing to please them," she says.

"I've never really thought about it like that before, but that's how it is."

Enough of the theory, what about some practical advice?

I know what not to buy - but that isn't very useful on its own.

"First of all, we need to talk about size," says Maria.

"What bra size is your wife?"

At this point, I feel very proud of myself.

I've snooped in my wife's underwear drawer and know the answer.

Not all Maria's customers show such foresight.

"Some men will cup their hands in front of my breasts and say: "About that size?"

Or they'll point to another woman in the department and say: "My girlfriend's a little bit bigger than her and a little bit smaller than you." (Maria is a 34DD.)

Knicker size is equally fraught with danger.

Maria has some useful advice: "If you don't know what size she is and you're not sure whether to go for the medium or a large, don't go for the large: because if you're wrong you'll be the one that ends up wearing them - on your head.

"It's better to flatter her by buying a smaller size."

If they are too small, your partner can always secretly come in and swop her briefs for a bigger size.

And honour is preserved.

Maria keeps on with the questions.

What colour is my wife's complexion? Her eyes?

How tall is she? What shape? What sort of job does she do - is she in an office all day?

I tell her that she's a brunette.

After a pause of no more than ten seconds, I remember she has hazel eyes.

And the office question is easy: no, she's a teacher.

I also dredge up the fact that my missus doesn't like thongs.

(Me neither, actually.)

"Some of them can be like cheesewire," admits Maria.

I recall that most of my wife's prettier knickers are shorts-style.

Maria again has a tip: "It's very flattering if you go for a style that is cut higher - that will accentuate the length of the leg."

All the while, Maria's eyes dart around the department for a suitable purchase.

She presents me with a shortlist - a wine-coloured lacefronted bra with a moulded half-cup from John Lewis's own brand (not very exciting), a smart but ultimately ordinary nude-coloured Calvin Klein number with a floral motif (dainty but dull) and...a gorgeous half-cup black moulded bra with small beige spots and delicate beige trimming.

It's from Elle Macpherson's Intimates range and I love it.

The knickers are hipster-style shorts - with the all-important high-cut leg.

It is pretty without being too girlie and it's sexy without being tacky. But it's black.

Doesn't that break Maria's first "Noah's Ark" rule?

Happily not: the beige spots are the get-out-of-jail card.

And anyway, the material is so soft and luxurious there's no way my wife won't like it.

Amazingly, the set comes to only £39.

And my wife's verdict (I presented her with her gift when I got home)? A no-question success - I can tell the difference between polite thanks and heartfelt happiness.

"It's lovely. Really pretty. I love it," she says.

Then she adds: "You've bought something I would've chosen myself."

Which I suppose was pretty much the idea. Only one problem - next Christmas, I'll have no excuse.

• THE John Lewis lingerie academy for men runs on December 13 and 20.