Tom Watson is shrinking, in every sense of the word. Labour’s deputy leader is shedding the pounds by cutting out sugar – and chronicling his weight loss in Instagram posts. Politically, too, the West Bromwich MP is something of a reduced figure. Party rule changes negotiated between Jeremy Corbyn and the major trade unions mean that while Watson is still the unofficial leader of Labour’s Corbynsceptics on the National Executive Committee (NEC), his influence there has waned.

Watson believes Corbyn’s unexpected election success means that he has earned the right to lead the party without facing plots and attempted coups. The leadership, for its part, has used its increased political clout to take greater control of Labour’s backroom operations. For most of the first two years of Corbyn’s leadership, pukka Corbynites were only really represented at Labour headquarters by the party’s digital team. Now the press team is increasingly loyalist, and the party’s permanent staff at its headquarters in London’s Victoria looks likely to follow suit.

The leader’s office even has its own channel on WhatsApp messenger, where senior staff broadcast to the rest of the shadow cabinet’s advisers. Although the purpose of the channel is serious, the tone is often light-hearted. David Prescott, one of Corbyn’s aides, recently warned staff not to respond to a Sunday Times inquiry about which pets were owned by members of the shadow cabinet. Andrew Fisher, Corbyn’s policy chief, popped up to reassure everyone that the Sunday Times’s “bark is worse than their bite”. (James Mills, John McDonnell’s press chief, added the less cerebral “Woof woof”.)

For a minority of Labour MPs, however, Corbyn’s growing hegemony and Watson’s acquiescence are no laughing matter. The deputy leader has been deliberately absent from several controversial votes and was notably silent when the leader’s office used its NEC majority to halt the election of a new chair of the party’s policy forum on 17 February. Why did Corbyn’s team want the contest stopped? Because its preferred candidate was about to lose. Ann Black, who has impeccably left-wing views but is one of the party’s few pluralists, was expected to defeat Andi Fox, who has similar politics but is regarded as more of a reliable factional operative. Although several MPs publicly voiced their displeasure, Watson was not among them.

Yet for all that some Labour MPs talk up the need for greater “courage”, “opposition” or “leadership” against the Corbyn project, their problem is that at least two-thirds of the membership is squarely behind him. The real battle facing Corbynsceptic Labour MPs isn’t a fight for control of the party or not, but whether the centre-left survives within Labour at all.

Most of Labour’s Corbynsceptics are more than aware of that, which is why they agree with Watson’s strategy. With the exception of perhaps three Labour MPs, there is no appetite for a new party, either. Opposition to a breakaway has two sources. Pragmatists fear that the strength of the Labour brand and the British electoral system mean that any new party is doomed from the get-go. More important, however, is the emotional connection that the majority of Labour MPs have to the party: most would rather have a limb amputated than leave. Therefore, the consensus among the leader’s critics is that the focus needs to be on building bridges so that, when Corbyn steps down or is defeated in 2022 (few Corbynsceptics expect Labour to win next time), a candidate from another tradition or faction can take over.

In theory, this argument commands the support of all but a handful of Corbynsceptic MPs. In practice, they can’t stick to it. They know that silence is their best route to power – but time and time again, the impulse to speak out becomes overwhelming. Some canny MPs limit their interventions: many will criticise the leadership only on Europe. Others will raise their heads above the parapet only when the party is insufficiently tough on members who engage in anti-Semitism. For others, it is abuses of power such as the one that occurred when the leadership stopped the national policy forum election. The problem, of course, is that these red lines vary from person to person. So instead of giving the impression of a group choosing its interventions carefully, the result is a cacophony of protest.

The same doublethink applies when Corbynsceptics look ahead to the next leadership election. With the exception of some of Chuka Umunna’s allies, who talk up their candidate’s ability to expand the party membership as Corbyn did, most Corbynsceptics believe that the path to victory next time must involve gaining the support of party members and trade unionists who backed Corbyn in 2015 and 2016.

The problem is that these same people tend to react angrily whenever a senior Labour politician does or says anything that might actually appeal to members. Currently in the firing line are Angela Rayner and Emily Thornberry, both of whom took to the airwaves to defend the leadership’s handling of the national policy forum election. Similar objections have been raised about Jon Ashworth, the shadow health secretary, and of course about Tom Watson.

In a way, Corbynsceptics have it easy: their options have been clear since Corbyn was re-elected as leader and even more so since the general election. Split and form a new party; try to overthrow the Labour leader a second time; or try to mend fences.

They have ruled out the first course of action and they know full well that the second is a suicide mission. That leaves only the third option. Yet the discipline needed for diplomacy and silence seems a harder diet for Corbynsceptics than Watson’s abstention from sugar.