function auth_val_postcode(formName, isRequired)
			{
			var fieldValue = document.forms[formName].postcode.value;
					if ((isRequired || fieldValue != '') && (!/^(GIR 0AA|[A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW]) [0-9][ABD-HJLNP-UW-Z]{2})$/.test(fieldValue))) {
												return errorMessage['postcode_xs:pattern'];											
											}
											
				return null;
			}