There is a 1.4% of the transaction total + 20 pence charge added to each order

To use this script add a html element to your form and paste this into it. Adjust the input names to match yours.

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script> <script type="text/javascript">$(document).ready(function(){
$('input[name="total"]').attr('readonly', true);
$('input[name="amount"]').keyup(function(){
var valone = $('input[name="amount"]').val();
var valtwo = .20;
var valthree = 1.014;
var total = ((valone * valthree) + (valtwo));
$('input[name="total"]').val(total.toFixed(2));
});
});</script>