The ad, called "the uncredible shrinking man", was created by Lucky Generals and will air tonight on BBC1. Ric Cantor directed the film through Hungry Man.
The four-minute spot is filmed in black and white, and has actors playing caricature versions of leading Conservative and Liberal Democrat MPs. The ad opens in a Cabinet Office meeting, where the Conservative Prime Minister and his cronies discuss policy changes that will protect the rich and harm the poor.
Clegg, the Liberal Democrat leader, initially tries to assert himself on things like tuition fees but soon drops his principles and begins shrinking, until he is no bigger than a pencil.
At the end of the spot, Clegg is left on his own, at the mercy of the Downing Street cat.
Helen Calcraft, one of Lucky Generals’ founders, said: "Party political broadcasts are notoriously dry, which means that few voters, regardless of their politics, engage with them.
"Of course, we have many serious policy issues to cover off — from income tax to student loans, the NHS to VAT — but we were determined to do so in an entertaining and memorable way."