"An endangered species kept against their will for the entertainment of others," Nic Dakin said. He meant the Liberal Democrats, and that made the House laugh. Everyone was in a very frisky mood for the liveliest Thursday afternoon the House has had for years. The Backbench Business Committee, under the chairmanship of Natascha Engel, has maybe not put a bomb under the House of Commons but has certainly lit a firework in it.

Mark Pritchard proposed his ban by denouncing No 10 ("He must really like animals," a colleague murmured). Pritchard told the House he'd been asked to withdraw his motion, that he'd been offered an incentive, a reward, a job if he would. He'd even been threatened. Someone in Labour, believing themselves to be shocked, barked "Good God!" That wasn't the only moral showmanship of the afternoon.

Pritchard said he'd come from a council estate rather than a landed estate but that his background had given him backbone! MPs needed spine, not jelly! His own spine was clearly enriched with marrowbone jelly!

The whips were said to be harshly whipping Tories against this backbench motion. MPs were scandalised. So much so that the whips caved by 4.15pm and offered – so Pritchard announced in an intervention – a free vote. "Some free votes are freer than others," Jim Dowd said darkly (a sometime whip himself).

Almost no one spoke against the ban, except Andrew Rosindell who made a technical term of himself. There was no evidence circuses were cruel to animals, he said, and because many of these lions and tigers were 10th-generation circus animals a ban would wrench them from the life they were used to. "If their rhythm of life were obliterated, you'd be being more cruel," he told a barracking House. And then: "I'm fed up with animals being used as a political football!" No, that would be cruel, actually. And very difficult to score goals.

But that wasn't the oddest thing said. Bob Stewart – an old soldier, still suffering shell-shock it seems – told us of his experience with a bear that wouldn't be tempted from his cage "even with honey". But, happy ending: "We ethnically cleansed that bear out of Bosnia, and he's now happy in a zoo in Amsterdam." It was the House's turn to be shell-shocked.

But it wasn't as good as the castrated monkey called Donkey, from Sheryll Murray. There isn't room for this sad story, but the monkey called Donkey is now living a fulfilled life among her constituents in Cornwall.

It was all a disaster for the Tory whips (they'll get the blame). But will the Government now act on this backbench vote, as promised? It could be a test for Cameron's grace in defeat.