Used by member's of Britain's right wing Conservative Party as a last resort when they have no valid defense or comeback; especially during Prime Minister's Question Time.
Weak leader Rishi Sunak seems particularly fond of using it despite the argument being largely irrelevant now as Jeremy Corbyn no longer sits as a Labour party member.
Background:
The animosity towards Jeremy Corbyn stems from a successful smear campaign orchestrated by the Conservative party, especially during the 2019 election campaign where it was aided by the UK's overwhelmingly right wing media including the supposedly neutral BBC.
Example of The Corbyn Defense:
"Let's not forget that the opposition wanted Corbyn as Prime Minister"