Sir Keir Starmer is looking for an "attack dog" deputy Labour leader and will not give Angela Rayner's replacement any formal government duties, The Telegraph understands.
The contenders competing for nominations from MPs to replace Ms Rayner as deputy leader of the party, after she was forced to resign over paying too little stamp duty on her second home, were reduced from six to five on Wednesday following the withdrawal of Alison McGovern, who serves as a junior minister with responsibility for local government.
The first tally showed Bridget Phillipson, the Education Secretary, is leading the pack, with 44 backers in the Parliamentary Labour Party.
Ms Phillipson already has a ministerial job, but Dame Emily Thornberry, Lucy Powell, Paula Barker and Bell Ribeiro-Addy all sit on the backbenches.
The sex of the candidates meets the parameters recommended by recent calls from Baroness Harman that the next deputy must be a woman. Lady Harman served in the role between 2007 and 2015 under Gordon Brown and Ed Miliband.
Senior Labour figures have been locked in discussion about what the deputy leader's responsibilities will be if a backbencher is elected, since Sir Keir has already handed Ms Rayner's former government role to David Lammy.
Party sources said the new deputy leader is likely to be tasked with being an "attack dog" for the party, and will be given responsibility for motivating campaigners ahead of the local, Scottish and Welsh elections in May.
Labour strategists are alarmed about the rise and continued success of Reform UK, which is around 11 points ahead in the polls, and the risk that the Green Party and Jeremy Corbyn's "Your Party" will steal support from Left-wing voters.
The deputy leader will therefore be asked to spend time in Labour headquarters, motivating staff and developing new lines of attack, while fronting the party's political attacks against opposition parties.
Since the rules of the deputy leadership contest were announced on Monday, the field has separated into a government candidate, in Ms Phillipson, and the backbenchers, including Dame Emily, Ms Ribeiro-Addy and Ms Powell, who served in the Cabinet until Friday.
Dame Emily, the frontrunner among the backbenchers, has pledged to fix the "mistakes" in the Government's strategy, which she said included cuts to the welfare budget, Downing Street's position on Gaza and "wealth inequality", which has been interpreted as a call for a wealth tax.
Ms Ribeiro-Addy, a member of the Socialist Campaign Group, has been more forthright, arguing that Labour "urgently needs to go back to the guiding values of our party and movement, and deliver an ambitious programme of popular, progressive policies". She said the party must oppose "genocide" and sanction Israel.
Some Labour backbenchers have said they will back a critic of the Government for the deputy leadership role, in the hope that they will act as a moderating force on Downing Street.
As deputy prime minister, Ms Rayner was invited to daily meetings at 8.30am in No 10, which gave her a ringside seat and significant influence on the Government's overall direction and policymaking.
She also sat on several of the most powerful Cabinet committees, including on national security and home and economic affairs.
However, the suggested job description for the new deputy leader, being worked on in the party's headquarters, will not include government business.
The new deputy leader will be asked to focus on party business, and will be expected to spend a significant proportion of their time outside of Westminster campaigning on the doorstep, and will inherit roles on the various internal democracy bodies within the Labour Party.
One of those bodies - the National Policy Forum - can develop policies approved by the membership, but the Government is under no obligation to adopt them.
Should Ms Phillipson win the race, she is not expected to receive a promotion and would retain her existing portfolio of education.
And should a backbencher beat Sir Keir's preferred candidate to the job, they are likely to remain a relatively marginal figure in Labour circles, more similar to the party chairman than a fully-fledged Cabinet minister.
This approach allows Downing Street to avoid a significant opposition voice in Whitehall and clip the wings of any firebrand who expects to change the course of government policy.
If anything, by forcing a would-be critic to repeat government attack lines each day, Sir Keir will have rid himself of a potentially troublesome backbencher.
With six weeks of canvassing left, Labour Party members would be well-advised to treat any candidate's pledge to shake up the Government with extreme caution. The members may have a say - but Sir Keir remains in control.