Almost 20 years ago, Margaret Thatcher went to the College of Bruges to deliver an address that was regarded as a call to arms against the relentless advance of the European Community and a rallying cry for national sovereignty. At that moment, the Conservative Party started to displace Labour as the principal and principled repository of European thinking.

David Miliband's sentences at the same venue yesterday were never destined to have anything like the same effect. His “vision” of Europe's future rejected the notion of a superstate but endorsed mild integration and supported the expansion of the single market to include North African, Middle Eastern and Eastern European states as, potentially, a step towards full EU membership. If he had a theoretical message to offer (after a little editing from Downing Street) it was about the need for Europe to exploit both “soft” and “hard” power to advance democracy.

The intriguing question in the corridors of power at home and for ambassadors looking in is whether Mr Miliband has hard, soft or minimal power over the direction of foreign policy. It is a question that is inevitably asked about every incoming foreign secretary. It was never evident what Margaret Beckett thought of the world (or vice versa) and whether she had authority independent of Tony Blair.

The debate on Mr Miliband's standing is sharpened, however, by two factors. First, he was relatively unknown before being placed in such high office at a youthful age and, secondly, he has to serve with a prime minister who has seemed interested in foreign policy in theory but less so in practice.

So Mr Miliband's clout and his influence have yet to be established. He is very much the post- modern Foreign Secretary with a taste for technological innovation. He has a rather silly blog that is more about burnishing his image than true democratic outreach. There are regular turns on YouTube, even if the audience secured is minuscule. Only on Wednesday, he, along with the foreign ministers of the Maldives and Malta, conducted what the Foreign and Commonwealth Office news department hailed as an “historic joint virtual press conference through Second Life to draw the world's attention to the devastating impact of climate change” (a pity that the FCO news release misspelt him as Mr Milliband). And he has two astute media advisers, perhaps inevitably dubbed Trinny and Susannah. But to the brutal, anyone on Second Life needs to get a life.

Climate change and the (welcome) prospect of Turkey becoming a part of the EU are long-term questions. The Foreign Secretary's significance today depends on the degree to which he and his department shape policy in Afghanistan, and influence an innovative debate over the future of Iraq. Mr Miliband must also take on the Department for International Development, which behaves as if it were a left-wing NGO, not an agent of British foreign policy. He should assume more of the lead on Pakistan, Iran and Iraq, not risk being seen as merely a middleman between Gordon Brown and Lord Malloch-Brown (to be dubbed “Mr Malloch-Miliband” would be fatal).

Being nice and bright and cheery is not enough in politics. Whether Mr Miliband can acquire pre-modern attributes - necessarily assertive and sometimes confrontational in Whitehall and in his dealing with other foreign ministers - will determine whether anything that he says or does in this post will endure.