private function addDescription(array &$gatewayData)
    {
        $payment = $this->owner->getPayment();
        if ($payment->Gateway == 'SagePay_Direct' || $payment->Gateway == 'SagePay_Server') {
            $gatewayData['description'] = sprintf(
                'Payment made on %s',
                date('D j M Y')
            );
        }
    }