function checkPostCode (toCheck) {
	
	/*==============================================================================

	Application:   Utiity Function
	Author:        John Gardner

	Version:       V1.0
	Date:          18th November 2003
	Description:   Used to check the validity of a UK postcode

	Version:       V2.0
	Date:          8th March 2005
	Description:   BFPO postcodes implemented.
    	           The rules concerning which alphabetic characters are alllowed in 
        	       which part of the postcode were more stringently implementd.
  
	Parameters:    toCheck - postcodeto be checked. 

	This function checks the value of the parameter for a valid postcode format. The 
	space between the inward part and the outward part is optional, although is 
	inserted if not there as it is part of the official postcode.

	If the postcode is found to be in a valid format, the function returns the 
	postcode properly formatted (in capitals with the outward code and the inward
	code separated by a space. If the postcode is deemed to be incorrect a value of 
	false is returned.
  
	Example call:
  
	  if (checkPostCode (myPostCode)) {
	    alert ("Postcode has a valid format")
	  } 
	  else {alert ("Postcode has invalid format")};
                    
	------------------------------------------------------------------------------*/

	  // Permitted letters depend upon their position in the postcode.
	var alpha1 = "[abcdefghijklmnoprstuwyz]";                       // Character 1
	var alpha2 = "[abcdefghklmnopqrstuvwxy]";                       // Character 2
	var alpha3 = "[abcdefghjkstuw]";                                // Character 3
	var alpha4 = "[abehmnprvwxy]";                                  // Character 4
	var alpha5 = "[abdefghjlnpqrstuwxyz]";                          // Character 5
  

	// Array holds the regular expressions for the valid postcodes
	var pcexp = new Array ();

	// Expression for postcodes: AN NAA, ANN NAA, AAN NAA, and AANN NAA
	pcexp.push (new RegExp ("^(" + alpha1 + "{1}" + alpha2 + "?[0-9]{1,2})(\\s*)([0-9]{1}" + alpha5 + "{2})$","i"));
  
	// Expression for postcodes: ANA NAA
	pcexp.push (new RegExp ("^(" + alpha1 + "{1}[0-9]{1}" + alpha3 + "{1})(\\s*)([0-9]{1}" + alpha5 + "{2})$","i"));

	// Expression for postcodes: AANA  NAA
	pcexp.push (new RegExp ("^(" + alpha1 + "{1}" + alpha2 + "?[0-9]{1}" + alpha4 +"{1})(\\s*)([0-9]{1}" + alpha5 + "{2})$","i"));
  
	// Exception for the special postcode GIR 0AA
	pcexp.push (/^(GIR)(\s*)(0AA)$/i);
  
	// Standard BFPO numbers
	pcexp.push (/^(bfpo)(\s*)([0-9]{1,4})$/i);
  
	// c/o BFPO numbers
	pcexp.push (/^(bfpo)(\s*)(c\/o\s*[0-9]{1,3})$/i);

	// Load up the string to check
	var postCode = toCheck;

	// Assume we're not going to find a valid postcode
	var valid = false;
  
	// Check the string against the types of post codes
	for ( var i=0; i<pcexp.length; i++) {
		if (pcexp[i].test(postCode)) {
    
			// The post code is valid - split the post code into component parts
			pcexp[i].exec(postCode);
      
			// Copy it back into the original string, converting it to uppercase and
			// inserting a space between the inward and outward codes
			postCode = RegExp.$1.toUpperCase() + " " + RegExp.$3.toUpperCase();
      
			// If it is a BFPO c/o type postcode, tidy up the "c/o" part
			postCode = postCode.replace (/C\/O\s*/,"c/o ");
      
			// Load new postcode back into the form element
			valid = true;
      
			// Remember that we have found that the code is valid and break from loop
			break;
		}
	}
  
	// Return with either the reformatted valid postcode or the original invalid 
	// postcode
	if (valid) {return postCode;} else return false;
}