EVER since the Earl of Sandwich slapped a piece of meat between two slices of bread so he didn't have to leave the gambling tables, we have been eating a rather strange concoction called a sandwich.

A sandwich can be any size, can contain virtually any thing and can be made from bread, wraps, pitta, naan or Lebanese bread, bagels, crepes, brioche, or baguettes, depending where you are in the world.

And we can't get enough of them.

Marks & Spencer, which claims to be the first retailer of pre-packed sandwiches, having launched six varieties in 1980, sells more than one-and-a-half million sandwiches a week.

During 21-years, the company has sold over two billion sandwiches and now sells more than 92 different types.

"As sandwiches have become more than just a lunchtime snack, customers are looking for more variety and interesting fillings," said a spokesman for Marks & Spencer, who added that the Onion Bahji Sandwich and the Big Chicken Tikka Naan were very popular.

This week is British Sandwich Week (May 14-20) and Marks & Spencer is celebrating by introducing a sandwich that reflects a British institution, the beef wellington sandwich.

Available for a limited period only, it is served on tasty harvester bread and consists of layers of medium/rare roast beef, rich farmhouse pate with duxelle mushrooms and sweet cure bacon with lettuce.

Sainsbury's has also launched a celebratory special, called The Big One, modelled on the enormous sandwiches typically found in New York.

Weighing almost half a kilogram, The Big One contains roast beef with caramelised onion chutney and traditional American mustard, layered onto Chicago flat bread, a slowly fermented bread.

"We trawled the streets of New York, eating our way through as many delis as possible to bring the concept of a truly authentic American sandwich to the shelves," said Sainsbury's sandwich buyer, Marcus Rees.

The kind of sandwich you choose depends on your mood and also your sex, according to research carried out by Sutherland Sandwiches.

Sutherland Sandwiches are produced by Hazelwood Chilled Foods, which claims to be the world's number one sandwich manufacturer.

"A sandwich not only says a lot about you as a person, but what frame of mind you were in when you purchased it," said marketing manager Richard Esau.

"There's a clear divide between women's attitudes to buying a sandwich compared to men. Women are more likely to buy a healthy sandwich than men, who often just want something to satisfy their hunger.

"However, women are also more prepared to indulge in something exotic, such as Thai chicken, compared to men who are likely to choose large, traditional meat-based recipes like sausage and bacon slices.

"Gone are the days when you could display the cheese varieties or all the egg options together - they need to be divided into categories such as 'healthy' or 'indulgent' to meet consumers' needs."

So next time you make your sandwich selection, beware what you are saying about yourself!