function checkPostCode (toCheck) {

  // 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);

  // 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;
}


function verifCO() 
	{ 
		if(document.form1.InvName.value == "" || document.form1.InvName.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter an 'Invoice To' name&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.Email.value == "" || document.form1.Email.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter your email address&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.InvS1.value == "" || document.form1.InvS1.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter an invoice address line 1&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.InvCity.value == "" || document.form1.InvCity.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter your invoice town or city&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.InvPost.value == "" || document.form1.InvPost.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter your invoice postcode&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.DelName.value == "" || document.form1.DelName.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter a 'Deliver To' name&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.DelS1.value == "" || document.form1.DelS1.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter your delivery address line 1&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.DelCity.value == "" || document.form1.DelCity.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter your delivery town or city&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(document.form1.DelPost.value == "" || document.form1.DelPost.value == " ")
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter your delivery postcode&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(!checkPostCode(document.form1.DelPost.value))
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter a valid delivery poscode&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else if(!checkPostCode(document.form1.InvPost.value))
		{
		document.getElementById('ErrorBox').innerHTML = "<span style='color: #ffffff; background-color: #ff0000'><b>&nbsp;Please enter a valid invoice poscode&nbsp;</b></span>";
		scroll(0,0);
		return false;
		}
	else
		{
		document.form1.DelPost.value = checkPostCode(document.form1.DelPost.value);
		document.form1.InvPost.value = checkPostCode(document.form1.InvPost.value);
		return true;
		}
	}