'I SPY STRANGERS'
Members of the public have not always been allowed to 
watch the House's proceedings - and the right to debate in 
private still exists. If an MP believes a debate should be 
conducted in private, he can shout 'I spy strangers' - and 
the Speaker will then propose the Motion 'that strangers 
do withdraw'. 

In practice, this rarely happens. The most recent private 
debates took place during the Second World War, for reasons 
of National security. However, 'I spy Strangers' is occasionally 
used as a device to delay proceedings or expressing indignation on a subject - though this is frowned upon by the Speaker.