IGNORE ABOVE!!!!
I have just tried it again, by reversing the parameters and this time it works properly!!
$WA_redirectURL = "cars_Update.php?CarID=".((isset($_POST["WADAUpdateRecordID"]))?$_POST["WADAUpdateRecordID"]:"") ."&tab=1#TabbedPanels1";
*&^%$ computers!!
Cheers
Chris