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);
        // 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 postcodes
      return valid;
 }