I have now got the order value to display on the confirmation email.
Please could you confirm that this is the correct way to do this, it seems to work OK.
Added a custom variable to the confirm page to be sent to worldpay as below
<input type="hidden" name="MC_ordervalue" id="MC_ordervalue" value="<?php echo $eCart1->TotalColumn("TotalPrice") ?>" />
<?php echo (number_format((isset($_POST["MC_ordervalue"]))?$_POST["MC_ordervalue"]:"",2))?>
to display the order value to two decimal places on the confirmation email which is sent to the customer.