Get Order subtotal in WooCommerce

I have a plugin that outputs a PDF of my orders. One of the sections displays the order total. Currently this displays the total, but I want it to display the subtotal (i.e. the order amount before any coupons etc are applied).

Can anyone help?

This is the current code:

    $order_total = is_callable(array($order, 'get_total')) ? $order->get_total() : $order->order_total; ?>

    <p id="order-total">
<b><?php _e('ORDER TOTAL:', 'woocommerce');?></b>
<span id="order-total-price">£<?php echo $order_total;?></span>

Updated:

You can use the WC_Abstract_Order method get_subtotal_to_display() to get and display the Order subtotal (but as it's a formatted price we need to clean it):

// Get the currency symbol
$currency_symbol = get_woocommerce_currency_symbol( get_woocommerce_currency() );

// Get order total
$order_total = is_callable(array($order, 'get_total')) ? $order->get_total() : $order->order_total;

// Get order subtotal
$order_subtotal = $order->get_subtotal();
// Get the correct number format (2 decimals)
$order_subtotal = number_format( $order_subtotal, 2 );

// Get order total discount
$order_discount_total = $order->get_discount_total();
// Get the correct number format (2 decimals)
$order_discount_total = number_format( $order_discount_total, 2 );

?>
<p id="order-subtotal">
    <b><?php _e('ORDER SUBTOTAL:', 'woocommerce');?></b>
    <span id="order-subtotal-price"><?php echo $currency_symbol . $order_subtotal;?></span>
</p>
<p id="order-total-discount">
    <b><?php _e('ORDER DISCOUNT TOTAL:', 'woocommerce');?></b>
    <span id="order-total-discount-price"><?php echo $currency_symbol . $order_discount_total;?></span>
</p>
<p id="order-total">
    <b><?php _e('ORDER TOTAL:', 'woocommerce');?></b>
    <span id="order-total-price"><?php echo $currency_symbol . $order_total;?></span>
</p>

Tested and works