The co-author of “Brown at 10” writes an open letter to the shadow chancellor:

Dear Ed,

I was not your headmaster, but as somebody who has written about you for many years it falls to me to say this: the time has come for you to fall on your sword.

After 20 unbroken years at the heart of politics, you need a rest. It was another age when in 1993 Geoff Mulgan, anxious to leave Gordon Brown’s side as chief adviser to found the think tank Demos, recruited you as his successor. After leaving Oxford, you had only the briefest time to work as an academic and a journalist on the Financial Times. You need to see more of life beyond the microworld of politics. Falling on one’s sword is never easy. However, quitting in the next few months until, say, 2017 would undoubtedly benefit your leader, your party, your wife and even yourself. Let me explain.

Ed Miliband would be a much stronger leader without you. He may think he cannot live without you, which is why he promoted you in January 2011 to shadow chancellor and recently pledged to stick with you. Yet he doesn’t need you, any more than Tony Blair needed Gordon Brown after a while: he merely couldn’t find it in himself to squeeze the trigger.

Forgive me, but you stop Ed breathing fresh air. With you close to him, his breath will always be stale and smell of a toxic brand. Without a prolonged period out of the public eye, neither you nor the party will ever rid yourselves of the opportunistic, negative and bullying image of the Gordon era. Yes, we both believe he was a better prime minister than the conventional wisdom says but it will take years for his achievements to be recognised properly and the stain of his modus operandi will never be eradicated.

Economic credibility would be more readily restored with your departure. Your critique of the government’s austerity strategy may never win back public trust and your proposals for the economy will never convince. Your credibility problem will only become magnified as the general election approaches. On Europe, despite your recent about-turn, the party will find it easier to commit to holding a referendum with you gone. Your patrician attitude not to trust the people will always make any call for a referendum from you sound hollow. Think how strong the appeal would be if Miliband offered the referendum that neither Blair nor Brown dared.

Without you, Labour could present itself as a clean party, free of the factionalism and brutalism that so tarnished it when Brown was boss and you were his consigliere. I know that you think you were really a very nice person all along, vulnerable with your own insecurities. Yet you need to redeem yourself and the atonement will never happen unless you disappear and return to public life with a fresh persona. The party would be more inclusive without you.

You say you like David Miliband, but his followers are not doing well under Ed, are they? The party would be much stronger with David back in the frame. So, too, would it with Alistair Darling returning to the front bench. In the event of a hung parliament, Labour would stand a better chance of putting together a workable coalition with the Lib Dems without you. Remember how in 2010 the Lib Dems didn’t trust Gordon or you? Nothing has changed, Ed.

What might you do during your long sabbatical? You have extraordinary intellectual and personal gifts. You could write a book (not, please, a memoir), as your mentor Gordon Brown did in 1986, about the Scottish politician and leader of the Red Clydesiders James Maxton. What about a biography of Brown? Not Gordon, nor your friend Nick, but George: you would learn much more about how factionalism damaged Labour in the 1960s. How about returning to academic life or journalism? Your experience would richly inform students and readers. What about a stint at a school? You would turn up your nose at Wellington College because we are independent, but how about our academy, Wellington in Wiltshire, founded when you were schools secretary? You could even study for an MBA and learn, unlike many others who become ministers, how to run large organisations.

I wish you’d listened when you ran education and I suggested that your two great opportunities for a legacy were to embed well-being deeply into schools and transform the relationship between the public and private sectors. You did little on either and it’s rather hard to remember much that you achieved of enduring benefit for young people. So it would be good to learn how to run an organisation. You could even run or work for a charity, as John Profumo did after his involuntary retirement from politics 50 years ago.

Yvette would not say it to you but, like many women working in the same organi­sation as their husband, she would be freer to think and act without you in her hair. You would have more time, too, for your three children. As a headmaster, I know how hard it is for children who have just one parent in the public eye. Having two is harder still and your family would only benefit with you being more present and less preoccupied.

The greatest beneficiary would be you. You may not see it this way now but I know you will in hindsight. A mentor of mine, Robert Skidelsky, suggested to your mentor Gordon that he take a sabbatical before becoming prime minister. Had he followed that advice, his premiership would have benefited. He would have had time to think through what he wanted to do with the power he had so long craved. As it was, he came to No 10 with the cupboard largely bare. If Labour loses in 2015, you will be blamed and your career will be damaged beyond repair. If it wins, you would return to the front bench in 2017 a redeemed and respected figure. You might even one day become leader, your long-held ambition. Oh, and don’t believe that guff about “skipping a generation”. The public will tire of young leaders, though it doesn’t yet realise it.

Others, including Ed Miliband, share responsibility for the Brown errors: you will earn praise for taking the hit. You are 46 this month. Your best years could lie ahead of you.

Yours ever, Anthony