For a Conservative Prime Minister who is reputed to share a good deal of his party's euro-scepticism, David Cameron seems increasingly to be discovering his inner Europhile. After a Brussels summit in which he made common cause with 10 other leaders to endorse an increase in the EU budget – an achievement successfully spun for British voters as a principled British triumph over EU extravagance – Mr Cameron entertained Chancellor Merkel at Chequers, before welcoming President Sarkozy to London for the signing of two treaties on defence co-operation. Old Europe would seem to be back in a big way.

Not, of course, that this is how the British-French agreements were presented yesterday. There was no hint that they might in time form the genesis of a European defence policy – though this should not be ruled out – they were seen rather as a bilateral arrangement between Europe's two largest defence players, both nuclear powers, reflecting a convergence of self-interest. Nor would it be wrong to regard the treaties in this light. Enemies they may once have been, and rivals in many ways they remain, but Britain and France share a respect for their own and each other's military heritage. They have been, and preserve, the sense of being global powers, and have unfinished business beyond Europe. They have also engaged in joint diplomatic visits, notably to Africa, in the recent past. There is more than enough common ground to make closer co-operation worthwhile.

There should be no mystery about why Britain and France have decided to enhance their co-operation precisely now. With budgets in both countries under strain, the defence sectors are under particular pressure to reduce costs – costs that are especially hard to cut because of their long-term nature, contractual obligations and the wide range of contingencies to be catered for. Both countries also have combat forces to maintain in Afghanistan, as well as smaller groups elsewhere, and want to avoid anything that would convey an acceptance of second or even third-class military status.

Co-operation, designed in such a way as to cover possible gaps and exploit complementary strengths, while not jeopardising independence of action, makes eminently good sense. But this does not mean that there are not questions to be asked about what the agreements – not just those enshrined in treaties – will mean in practice. Collaboration on nuclear testing technology, where France is very far advanced in computer simulation, is a quite specific step forward. Provision for joint training and for special forces to work under British or French command may make for greater operational effectiveness. But troops from both countries are by now quite used to working alongside others as part of international alliances. So this may not represent a great change.

Naturally, misgivings were voiced, both in anticipation of yesterday's summit and after the fact. Old enmities were recalled to cast doubt on the feasibility of closer British-French cooperation, while practicalities were also queried. The prospect of a single, shared, aircraft carrier at sea at any one time prompted a pointed enquiry about what might happen if a new Falklands crisis erupted when only the French carrier was available. To which there is an answer that Mr Cameron, briefly reduced to ambiguity, could not give – though it is the truth.

The time for Falklands wars, as for new Iraqs or even Afghanistans, is over. The future of Britain's defences may not yet be as European in complexion as it could and should be, but the principle of seeking allies across the Channel, rather than across the Atlantic, has now been set, and that marks a historic shift.