He's back and he's angry. Forget about Michael Howard. Tony Blair's biggest problem for now looks - again - to be relations with his Chancellor. Anyone who thought Gordon Brown was going to return from his happy and richly deserved paternity leave a politically mellowed man, had better think again.
Bestriding the left-right media spectrum like a colossus, Brown yesterday scored two palpable hits on the front pages respectively of The Guardian and The Daily Telegraph. To the first, his allies let it be known that he had twice been refused nomination by Tony Blair to the once mighty National Executive of the Labour Party. To the second he "exposed a growing rift between the Treasury and No Ten" (the paper's own words) with an article looking ahead to the planned new constitutional EU treaty and insisting it must ditch "the old flawed assumptions that a single market should lead inexorably to tax harmonisation, fiscal federalism and then a federal state". And this came hard on the heels of a BBC interview with the Chancellor which reflected his deep hostility to certain parts of the proposed treaty.
Just at the point that the Conservatives show every sign of coming together, in other words, the schism at the very top of government is graphically exposed once again. While the first story may seem to concern an extraordinarily arcane dispute about an inner party body most were only dimly aware still existed, it's difficult to think of anything which has more infuriated Mr Brown, even in the long history of the clashes between the two most important men in British politics.
But it was the (unconnected) remarks on Europe which were most immediately reverberating across Whitehall because they appeared to cut so directly across Mr Blair's basically upbeat assessment of the treaty negotiations. As the deeply eurosceptic Telegraph pointedly concluded its welcoming editorial: "Mr Brown seems to be calculating that Mr Blair's refusal to concede a referendum on the European constitution could be his Achilles heel. If the constitution matters as much as Mr Brown now says it does, why is Mr Blair refusing to give the country a vote on it?"
The fact that this is the analysis of the newspaper which published the Chancellor's article doesn't it make it right. But it mirrors the darkest fears of some in the Blair circle, namely that Mr Brown thinks that Mr Blair could be fatally weakened by his refusal to hold a referendum in the face of a clamour from the press and opposition. Or even more so by being - eventually - forced into holding a referendum he could actually lose. And that he is therefore, albeit indirectly, fuelling just that clamour.
To this, of course, there is an answer from inside a dismissive Treasury. Which is that whatever differences of tone and style within the Government there are none on the basic policy; namely that Britain must retain its veto on anything to do with tax - which along with a clarion call for economic reform to cope with global competition in the EU, is the main purpose of Mr Brown's new démarche. That by being upfront and aggressive in laying down the policy in this way, the Chancellor is maximising the chances of the British treaty victory he is convinced will be secured. That this was exactly how Mr Brown won the day last year, with a tough and public stance on a savings directive which might have resulted in banking business being lost to outside the EU. And that Mr Brown's call for wholesale reform of the ludicrously rigid EU stability pact is backed by a growing consensus in Europe.
This isn't baseless; but it isn't the only way of seeing the issue either. To take one example, and unfashionable as it is to say so, it isn't clear the most contested article of the draft treaty is quite the wholesale affront to national sovereignty its critics depict it as. It allows the EU to act collectively against a tax wheeze only if every member state agrees unanimously that it distorts the single market - an entity every British leader from Margaret Thatcher on has deeply believed in. Only then is any action to be taken by majority voting. And some in the Government doubt that the search for changes in wording designed to tighten this up still further will be made any easier by Mr Brown's strident demand for a wholesale veto of the clause.
But that's not all. It's hard to escape the conclusion that Mr Brown has been raising the rhetorical stakes in all this to win the heart and soul of the only two men who many top Labour politicians take as seriously as the party itself - Rupert Murdoch and Paul Dacre the editor of the Daily Mail.
Of course you can argue that given both The Sun and the Mail have afforded a vigorous welcome to the Tory leadership of Michael Howard, it helps to muddy the waters by sounding - on occasions and for all his (well founded) protests that he is really a pro-European - almost as bulldog-eurosceptic as Mr Howard is.
But you can also argue that it sits uneasily with the Chancellor's - commendable and increasingly timely - argument inside the Government that Labour needs to set out clear dividing lines on domestic policy between it and a newly invigorated Conservative Party, if you then go on to blur them on Europe. Particularly when your insistence on unbridled tax competition, if carried to its absolute limits, might threaten to erode the basis of a welfare state - not exactly a left-wing idea.
This isn't remotely to suggest that Mr Brown is wrong to be watchful or that there aren't elements in the draft treaty that are rightly unacceptable to the British Government as they stand. But even if their differences on Europe really are at bottom presentational - and that isn't certain - it is still painfully clear that Chancellor and Prime Minister are singing different tunes.
Especially as all this has accidentally - but combustibly - coincided with an extraordinary row over the national executive. A row which it now turns out was simmering at the party conference when Brown made the speech that brought accusations of disloyalty to Mr Blair. The row is deeply embarrassing to Douglas Alexander, the able young Brown ultra-loyalist, who has been appointed to the NEC by Mr Blair and is facing the wrath of his idol for accepting. It is almost as embarrassing for Ian McCartney, who goes on the NEC as party chairman and is in trouble with his own close ally John Prescott, who has been backing Mr Brown's claim to membership.
Mr Brown's allies believe the party will blame Mr Blair for autocratically denying him the role in developing party organisation, membership and strategy an NEC seat would give - not to mention Mr Blair's decision to chair an election committee Mr Brown presided over in 1997 and 2001. Mr Blair's allies believe he has the right as leader to bring on the cadres from the next generation of top Labour figures. The wider electorate will find the dispute baffling if not downright petty. But that's not really the point. Which is that the tensions between Mr Brown and Mr Blair have rarely, if ever, seemed as open or as dangerous - to both men.