If I add it to the translation override then the information will also be displayed if the user chooses to pay by bank transfer.
I have managed to solve it by overriding the Order Creation Notification email and adding 'or $data->order_payment_method=="check"' as follows. . .
<?php
if($data->order_payment_method=="banktransfer" or $data->order_payment_method=="check"){
$class = hikashop_get('class.payment');
$payment = $class->get($data->order_payment_id);
$payment->payment_params = unserialize($payment->payment_params);
echo $payment->payment_params->information;
}
?>