Unity was supposed to be one of New Labour’s defining characteristics. Back in the 1990s, it helped differentiate New Labour from the caricature of Divided Bad Old Labour – as well as from the Conservatives, then widely seen as hopelessly split. 
 
The latest data from the House of Commons shows that those days are now well and truly over. In the parliamentary session just ended, Gordon Brown’s second complete one as prime minister, Labour MPs defied their whips on 74 occasions, a rebellion in 30% of Commons divisions. Each of the four sessions since the 2005 election has now seen a rebellion rate of between 20 and 30%, and the parliament as a whole is currently averaging 27%, on course to be the most rebellious in the post-war era. In absolute terms, that record has anyway already been achieved; the 2005 parliament has seen more revolts against the whip by members of the governing party than any other post-war parliament.
 
The good news for the whips was that most of the rebellions were not large. Some 42 out of the 74 revolts consisted of fewer than 10 Labour MPs. And although a total of 102 Labour MPs voted against their whips, frequent rebellion remains concentrated amongst a small group of Labour MPs. The top 10 rebels in the session accounted for marginally under half (46%) of the total rebellious votes cast; the top 20 accounted for exactly two-thirds (66%) of the total. John McDonnell took the top spot as the most rebellious Labour MP, clocking up 46 dissenting votes. He was closely followed by Jeremy Corbyn on 45. Corbyn’s total number of votes against the whip for the Brown administration alone has now passed the 100 mark, with more than 400 in total since 1997.
 
The problem for the whips comes when discontent seeps out to a broader group than the most rebellious 20. On two occasions it became serious enough to result in defeat, over the Gurkhas and the Parliamentary Standards Bill. Gordon Brown thus continued the sequence, since Heath in the 1970s, of prime ministers suffering at least one defeat as a result of backbench dissent. But the defeats were just the tip of the iceberg. More significantly, the government has begun to engage in a series of U-turns on key aspects of its policy programme – most obviously on Royal Mail where the threat of a defeat was enough to shelve the plan. 
 
The whips also faced a new second front, as rebellious Labour backbenchers started supporting Conservative and Liberal Democrat Opposition Day motions. Since Brown became prime minister in June 2007, there have 23 separate Labour rebellions on Opposition Days. Compare that with the first Blair parliament from 1997 to 2001, when there were only two Labour rebellions on Opposition Days involving only two MPs. The defeat over the Gurkhas was just the most high profile example of this. Others included Heathrow, Iraq, carbon emissions, Equitable Life – and the Territorial Army, where the threat of defeat was enough to provoke another U-turn.
 
Even if the parliament’s final session sees relative calm – and final sessions usually do – we should still expect the 2005 parliament easily to become the most rebellious of the post-war era. And after the election? That will depend on what happens at the polls. Should Labour survive, expect backbench dissent to continue, at the same, if not higher levels. A Conservative government can expect to enjoy the sort of honeymoon with their backbenchers that new governments traditionally do – helped in this case by the fact that more than half of Cameron’s MPs will be newly elected and much more docile. But like all honeymoons, backbench ones end eventually, as New Labour’s did.