Allies of Gordon Brown have called for an orderly transition of power when Tony Blair stands down, and warned that ultra-Blairites risk plunging Labour into a civil war.
The Brown camp raised the prospect that Labour would suffer the same divisions that troubled the Tories after Margaret Thatcher was ousted by her own party in 1990.
Brownites denied they were threatening Mr Blair, saying they were responding to criticism of the Chancellor by Stephen Byers, the former cabinet minister and a Blairite "outrider", who called for inheritance tax to be scrapped.
Ed Balls, the Economic Secretary to the Treasury and Mr Brown's closest ally, called Mr Byers a "maverick" and urged Labour to reject "factionalism". He told BBC Radio 4: "I think people remember what happened to the Tories in the late Eighties and early Nineties when their transition descended into division. To allow factionalism to take over would be unforgivable. There are a few maverick voices but... the vast majority of people in our party want a united transition."
Mr Balls coupled his criticism of Mr Byers with an attack on Tory plans to scrap stamp duty on share transactions. He said: "We have seen in the last few weeks, both from Stephen Byers and from the Tories, proposals for large and unfunded and uncosted tax proposals on inheritance tax or on stamp duty ... To go down the route of short-term sectional gestures on taxation would be exactly the wrong way to make sure we can address these long-term policy issues."
Some Blairites accused Mr Brown of appearing to take succession for granted. They warned that he was in danger of losing support among grassroots Labour members who wanted a say about the party's next leader.