function validatePostCode(postCode){
	
	  // 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);
	  
	  // Overseas Territories
	  pcexp.push (/^([A-Z]{4})(\s*)(1ZZ)$/i);

	  // 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{
  	alert(PLEASE_ENTER_POST_CODE);
  	document.postcode_search.post_code.focus();
  	return false;
  }
}