Jose Manuel Durao Barroso looks like a man who intends to be in charge. The new president designate of the European Commission is stamping his mark early on his motley group of 24 commissioners, insisting they will be a team and that he's the leader. If he can keep this up, the Union may have a forceful, dynamic Commission for the first time in 10 years.

It's early days yet, but Barroso could be a Delors Mark II, driving forward a strong European agenda. If so, this would be a real counterblast to the haphazard, gaffe-prone leadership of Romano Prodi and to his lacklustre predecessor, Jacques Santer, who presided over the unprecedented mass resignation of the Commission in 1999.

Tony Blair is cheering Barroso's allocation of the powerful trade portfolio to Peter Mandelson. But a strong, active, independent Commission president may not be what Blair had in mind as his ideal backdrop to the UK referendum on the EU's new constitution.

Barroso has certainly hit the ground running. In handing out jobs to the new commissioners, he has not only stood up to the larger member states, refusing them their first-choice jobs, and ensuring a good deal for the smaller states, but he's already squaring up to the senior officials in the Brussels bureaucracy. Barroso has insisted, for instance, that all commissioners are located as a team in one building - aiming to avoid the poor co-ordination and growth of fiefdoms that characterised the Prodi Commission.

The Blairites are hoping that Barroso will drive a UK-style economic reform agenda, under the banner of the so-called Lisbon strategy, and that this will provide welcome mood music for the referendum campaign - proving that Europe is going "our way".

But the reality may prove different. The rest of Europe is not fervently aiming to imitate British economic policies. It was former Portuguese leader Antonio Guterres, mastermind of the Lisbon strategy in 2000, who insisted on softening UK ideas on economic liberalisation by adding an equal commitment to social cohesion and full employment. Barroso has also stressed the importance of social Europe.

Nor is Peter Mandelson well positioned to argue the British economic case: the trade job will keep him busy - and travelling - 24/7. Other commissioners may have much more direct influence on how economic and social policies are taken forward.

Barroso's creation of a new commissioner to sell Europe to its citizens, Sweden's likeable Margot Wallstrom, may also cut two ways for the UK referendum campaign. Such a post is long overdue to tackle the normally clumsy or absent communication skills of the Commission. And the Commission could play a crucial role in rapidly rebutting myths on the new constitution as they appear. But a high-profile Commission answering back to British sceptics may be gladly seized upon by the Tories and a hostile media as proof of Brussels' dominance.

Recent pronouncements by pro-European Blairites such as Peter Hain and Denis MacShane suggest an emerging strategy to emphasise holding the Commission to account, including possible appearances of commissioners before Parliament. More accountability is a good idea. But this too could backfire. What Blair really wants, it seems, is a low-profile, accountable Commission effectively monitoring observance of the EU's rules in the single market and elsewhere. Yet Commons sessions with commissioners may only further highlight what a powerful, political pan-European body the Commission is. For what the Blairites try to hide is the fact that the Commission is indeed a quasi-government; it has the sole right to propose laws across the Community's policy areas. Under Delors, it was the Commission that drove forward the single market and the euro. The confidence with which Barroso has launched his presidency suggests we are about to see a tough, political Commission pushing forward new European strategies across the board. It will be more Delors II than Prodi II.

If Barroso can build good relations with the member states, this could be just what Europe needs to revitalise itself and prove its relevance to a suspicious public. But, for Blair, it may present an unwelcome challenge. With a highly visible Commission under strong leadership, the Prime Minister may face running the referendum campaign based on telling the truth about Europe as it really is - not Europe as he would like it to be, or as he thinks the voters would like it to be.

The writer is a visiting fellow at the LSE's European Institute