Thursday's Commons debate on banning the use of wild animals in circuses marked a tipping point. Not so much because of the substance of the issue - a recommendation about the fate of 30 or so animals in four circuses is not a government-breaking issue, and no-one pretends otherwise - but because of the blast of fury that met a government attempt to impose a three-line whip on a backbench debate on an issue well outside the great sweep of national policy.

In scenes unimaginable a few years ago, backbench MPs told the whips where to get off, one Conservative backbencher implicitly contrasted his humble origins with those of the prime minister, and almost every MP in the Chamber roared their approval.

To be sure, after all the doom and gloom parliamentary business of recent months, economic woe, endless job cuts, intricate and controversial reform bills on everything in sight, tribal warfare in Westminster and actual warfare in Libya and Afghanistan, there was an element of light relief about Thursday's debate.

But there was also a clear assertion of backbenchers' rights against a clear attempt by the government to assert its will. The Speaker refused to call a Government amendment, the backbenchers made it plain they were not going to do as they were told, and the whips were left to save what face they could, with a last minute concession of a free vote.

Parliament is starting to matter more; the question is whether this new-found assertiveness will be bottled up in Thursday afternoon debates of limited significance - prisoners' votes, MPs expenses and now circus animals - or whether it will spill out into general business.

Low level rebellion by MPs on either side of the Coalition has been pretty commonplace from the outset. The next big test may come when MPs finally get a chance to vote on the Statutory Instrument to hand the IMF an extra £9 billion from the British taxpayer - a proceeding viewed with great suspicion by the Tory right.

And how about this for a longer term bet: Nick Clegg proposed giving individual taxpayers shares in the mega-banks nationalised to save them during the Credit Crunch - the Conservatives are unenthusiastic; what if a Lib Dem amendment went down to some finance bill to mandate a share distribution, rather than allow the government to sell off the shares, with a view to funding a pre-election tax cut? What then?

A rebellion on that issue towards the end of this parliament could have pretty interesting ramifications, as the election approached.