Restaurants also know that most diners are too shy or embarrassed to ask for the price of the special - and, guess what, the waitress forgot to mention what the dish will cost you.

London - What’s so special about a restaurant’s “daily special”? It’s a familiar ritual. You’re sitting down, you’ve been handed the menu and the waitress launches into a florid description of an item that isn’t printed on the sheet she gave you.

If you’re lucky, the “special” is just that, something delicious that the chef has whipped up from fresh ingredients that caught his eye at the market this morning.

But very often the special - or “chef’s recommendation”, or “dish of the day” - is special only because it’s the most profitable item on sale, and the restaurant knows it will sell many more if the waitress singles it out for attention.

Restaurants also know that most diners are too shy or embarrassed to ask for the price of the special - and, guess what, the waitress “forgot” to mention what the dish will cost you.

The fake special is just one of the secret weapons restaurants deploy to make us spend more than we intend to when we go out to eat. In fact, the tricks begin as soon as you’re handed the menu, according to William Poundstone, author of Priceless: The Myth Of Fair Value, a new book on how businesses exploit their customers. He has spent years examining the psychology behind “menu engineering”. That’s the name of the secret way restaurants try to encourage us to choose the most expensive dishes they sell.

And because we don’t know they’re doing it, they’re nearly always successful.

For, whether we like it or not, every time we go out to eat, therestaurants are playing mind games with us - while we remain, mostly, innocently oblivious.

“People rarely go into restaurants knowing exactly what they want to order or how much they want to spend,” explains Mr Poundstone. “And we can be influenced by all sorts of things that we’re not aware of.”

At the centre of all this is the humble menu. You might think that the restaurant menu merely tells you what items are available in a certain establishment.

Actually, it is a very sophisticated piece of advertising. In fact, it’s the only piece of advertising that restaurant owners can be certain their customers will read.

As a result, restaurants invite in ‘menu consultants’ whose job it is to lay out a menu that will persuade you to spend more money than you’d expected.

You may, for instance, have noticed that increasingly the prices on menus no longer employ the pound sign - or even any evidence of pence. Where once a steak might have cost you “£16.00” now its price is stated as “16”.

Pound signs are disappearing from menus as quickly as cod are vanishing from the oceans.

And not just at fashionable restaurants. There are no pound signs at Carluccio’s, Byron, Giraffe or Cafe Rouge either.

This is not a coincidence. A study by Cornell University’s Centre For Hospitality Research in America found that when, in a similar move, dollar signs were left off a menu, sales increased by eight percent. Why so?

Simple, says Poundstone. “The more space you devote to something on a menu, the more people pay attention to it.

“So if you have a pound sign and the number of pence, it takes up more space on the page - and more space in your mental attention.

“And obviously the restaurant does not want you to choose your food on the basis of price.”

That’s also the reason why menus very often feature the items and their prices centred on the page, rather than having the prices all lined up in a tidy column on the right-hand side. If all the prices appear neatly one above another, says Poundstone, that just invites us to compare one against the other - which is the last thing the restaurant wants us to do.

For that same reason, you now never see dots leading the eye from the description of the item to the price.

Another key trick is known as ‘anchoring’. This is where a restaurant places a highly expensive dish prominently on the menu - solely in order to make the other dishes nearby appear relatively cheap.

At Marco Pierre White’s Marco Grill in London, there’s a 35oz Tomahawk steak on sale for £70. Restaurants do not expect to sell many of these costly “anchor” items, says Poundstone.

That is not their job - instead they are simply there to make the other dishes look like good value.

Suddenly spending £21 on a plate of Marco’s grilled Dorset lemon sole doesn’t seem so outlandish.

A lot of research has also gone into where we look when we first open a menu. It’s estimated that we read a menu for 109 seconds on average.

Studies have shown that when presented with a list we remember best the item at the very start, and the one at the end - it’s the way our memories work. We will also turn our eyes first to the top right-hand corner of a page in front of us, whether it be a double-page or single-sheet menu. So that corner, of course, is usually where the most profitable items are placed.

Poundstone says some of the other techniques are so commonplace, they seem unremarkable. Why might an item on the menu have a box around it? It’s not because it’s a dish the chef is particularly proud of, it’s because it earns a high profit for the restaurant.

Alternatively, the menu might use other methods to draw our attention: an item in a different colour; an accompanying illustration; a different typeface.

Professor Charles Spence, a psychologist at Oxford University, is the co-author of The Perfect Meal: The Multisensory Science Of Food And Dining, and alert to the techniques in play.

“I was in the burger restaurant Byron the other day,” he says. “The menu is all in black and white, except for one item, which is highlighted in bright red. And it’s their most expensive item.”

Professor Spence says that people are also likely to spend more if menus - and especially wine lists - are heavy to handle. And of course, even the words that menus use can persuade us to splash out.

At the restaurant chain Giraffe -which was bought last year for £49-million by Tesco, a company that knows all about parting us from our cash - the toast is “artisan sourdough toast”, the chicken nuggets have a “sesame crunch coating” and the salsa is “fiery red roasted chipotle salsa”.

Meanwhile the bresaola at Jamie Oliver’s Jamie’s Italian is “elegant slices of cured beef” and at West End eaterie The Ivy, in London, there’s an “heirloom tomato salad” and the carrots and beetroots are both labelled “heritage”.

Professor Spence says: “There’s research that demonstrates that if you give food a more descriptive label, people will enjoy it more - and they’ll also pay more for it.’ One common example of this is to attach somebody’s name to a dish. At Randall & Aubin restaurant in London’s Soho, they serve ‘slow roast Aubrey Allen pork belly”.

Few, if any, of the punters will realise who Aubrey Allen is. For all anyone knows, it could be the name of the boy who sweeps up the pork fat in the abattoir.

In fact, it’s the name of the butcher - based in a Coventry business park - who supplied the meat.

“This is a classic technique,’ says Professor Spence. ‘It could be any name there at all. But attaching the words ‘Aubrey Allen’ makes the dish feel like it’s more carefully chosen. It’s not just any old pork belly. And that allows them to put a premium on it.”

If it’s any comfort, it’s not just us poor punters who are victims of these mean tricks.

Restaurateur Russell Norman is the owner of a string of successful restaurants in London, including Polpo in Notting Hill. He is also innocent of all the sales ploys detailed here (except one: his menus do not use pound signs).

“My pet hate is the use of hyperbole on menus,” he says. “When chefs or restaurateurs describe dishes as ‘delicious’, ‘mouth-watering’ or ‘gorgeous’, I always think: ‘How dare you! I will be the judge of that, thank you very much.’”

But the other day, while on holiday in New York, even he fell victim to “anchoring”.

Visiting a restaurant, he was mulling over which wine to choose from a list which featured several bottles that cost $2 500 (£1 500).

“And because they had so many bottles that cost so much, I ended up buying a bottle of wine for $90 (£54). That’s nearly double what I’d normally spend. But they’d made it look cheap by comparison.

“I’m a restaurateur - and I was still suckered!” - Daily Mail