What is a sandwich?  By which I mean in generally accepted English
(UK) how many slices of bread constitute a standard sandwich?
Is a standard sandwich two slices of bread, one on top of the other?
If so does it become two halves of one sandwich if you cut it in half?
Or is a sandwich one slice of bread, cut in half and place on top of
one another, or folded over?
Alternatively, is a sandwich one whole object (ie one sandwich would
become two if you cut it in half) thus having nothing to do with bread
quantity?
Or is it something else all together?
I am looking for something of a definition in common UK English,
rather than general usage.  Though in some circumstances general usage
of language may constitute a definition where one does not exist.

Dear Inchhigh, 

The Cambridge Advance Learner dictionary (GB English disctionary)
defines a sandwich quite summarily:
"Two pieces of bread, sometimes spread with butter or margarine, and
with some other usually cold food between them". (SOURCE: Cambridge
Advanced Learner's Dictionary
<http://dictionary.cambridge.org/define.asp?key=69754&dict=CALD>).
This is also the Oxford definition ("an item of food consisting of two
pieces of bread with a filling between them",
<http://www.askoxford.com/concise_oed/sandwich?view=uk>).

"Pieces" could be of course interpreted as slices, but also as pieces
of slices (e.g., halves of a slice), with some sort of food between
them.

However, an "Open Sandwich" is defined by the same dictionary as "a
single slice of bread with various types of food, such as cold fish or
meat, on the top" (SOURCE: Cambridge Advance Learner's Dictionary,
<http://dictionary.cambridge.org/define.asp?key=55625&dict=CALD>) and
again, by Oxford, as "a sandwich without a top slice of bread."
(SOURCE: Oxford English Dictionary,
<http://www.askoxford.com/concise_oed/opensandwich?view=uk>).

From the definitions of an "Open Sandwich", one could *assume* that by
"pieces" in the original definition, the intention is to slices.

American dictionaries use the following definitions: 
"a piece of meat or other food placed between two slices of bread.
Although food in this form has long been used, the term sandwich
originated in the 18th cent. It is named for John Montagu, the 4th
earl of Sandwich, an inveterate gambler who ate informally at the
gaming table rather than stopping for the set meal." (Answers.com:
Encyclopedia information about sandwich, The Columbia Electronic
Encyclopedia, Sixth Edition Copyright © 2003, Columbia University
Press. Licensed from Columbia University Press.
www.cc.columbia.edu/cu/cup/)

"#

   1. Two or more slices of bread with a filling such as meat or
cheese placed between them.
   2. A partly split long or round roll containing a filling.
   3. One slice of bread covered with a filling." 
(SOURCE: Answers.com, Dictionary definition of sandwich
The American Heritage® Dictionary of the English Language, Fourth
Edition Copyright © 2004, 2000 by Houghton Mifflin Company. ).

The "slice" element is then, central here. Ironically, it is in the
US-English that "non-Sandwiches" are considered to be so: "The term
"sandwich" has been expanded?especially in the United States?to
include items made with other "breads" such as tortilla, rolls and
focaccia. Thus hamburgers and "subs", for example, are called
"sandwiches" in the United States, although not in most
English-speaking countries (since they are not made with slices of
bread from a loaf)." (SOURCE: Wikipedia,
<http://en.wikipedia.org/wiki/Sandwich>).

Finally the British Sandwich Association (you've to admit that you had
no clue that they've ever existed!) does not define sandwich, but
states in its consumer section "Making a sandwich is easy.  Simply
take two slices of bread, butter one side of each, add some slabs of
cheese and a bit of lettuce and tomato for colour, and you are
there?.. or are you?" (SOURCE: "Creating the Perfect Sandwich",
British Sandwich Association,
<http://www.sandwich.org.uk/infocentre.asp?param=view&id=80>). On the
other hand, on their homepage, they display those triangles sold in
Supermarket chains on its site, which are obviously halves (but four
triangles make two slices, right?).

British Sandwich Association - Homepage
<http://www.sandwich.org.uk/> 

I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it. My search terms:
Sandwich

Thanks for the quick response. My disappointment is that I may have
been proved wrong in my arguement that a sandwich requires only one
slice.

Thank you for the rating, and don't give up your hope - what about an
open sandwich? cucumber sandwiches?

I think there is a very interchangable use of slice and piece of bread
in the dictionaries descriptions.  Very seldom will you find an open
sandwich served on a whole slice of bread, unless it is meant to be
eaten with knife and fork.

I would consider anything a sandwich that was served or sold as ONE
sandwich.  If and up-market lunch store sells just a triangle (two
half slices) as one, then it is a sandwich.  Other places will make
you a andwich with two slices of bread and then cut it into two
triangle and never think of selling just one triangle.

Back in the 1950s, the airlines agreed that tourist class would be
only served sandwiches, which some then interpreted to mean one slice
of bread under a hot meal of meat, vegies and potatoes.
So take your pick.  myoarin