function validate_postcode(field) {
	var postcodeFilter = /[a-z0-9]/i;
	var illegalChars = /[\!\"\`\$\%\^\@\_\-\'\|\&\*\+\=\{\}\~\#\?\(\)\<\>\,\.\;\:\\\/\[\]]/;
	var first_char = field.substr(0, 1);
	var numbers = '1234567890';
	var postcode_value = '';
	var counter = 0;
	var positions = new Array (field.length);
	
	for (x = 0; x < field.length; x++) {
	  if (numbers.indexOf(field.substr(x, 1)) != -1) {
	    positions[counter] = x;
	    counter = counter + 1;
	  }
	}
	
	//document.search_form.postcode_F.value = postcode_value.toUpperCase();
	//alert (' -' + document.search_form.postcode_F.value + '-\n');
	
	if (!postcodeFilter.test(field) || field.match(illegalChars) || numbers.indexOf(first_char) != -1 || counter > 3 || (counter == 0 && field.length > 2) || (positions[0] > 2 && field.length > 2) || (counter < 2 && field.length > 4)) {
		return 0;
	} else {
		return 1;
	}
}