The Lisbon treaty is a muddle, and the worst consequence for Britain – and Europe – is the legal uncertainty that will follow. Britain’s prized opt-outs are valuable, but they do not shield it from that unpredictability.

This treaty is, in nine tenths of its prescriptions, the same as the ill-fated constitution that the Dutch and French rejected in 2005. There is no point dissembling about that.

Nor is the main reason put forward for its existence a good one: that an EU of 27 members would grind to a halt without it. The longer that has passed since the accession of ten new members in 2004 and Romania and Bulgaria at the start of this year, the clearer it is that this isn’t happening.

Nor has the final version satisfied the aims of simplifying the EU’s legal framework, handing back powers to member states and bringing Brussels closer to citizens by making its workings more transparent. The compromises needed to agree it have been achieved at the price of ambiguity.

The new treaty does make useful changes. Most important, it gets rid of the convention that each country holds the presidency for six months in rotation. Yesterday’s signing ceremony happened in Lisbon, absurdly, because Portugal, in the presidency, did not want to surrender the glory to today’s meeting of the same leaders in Brussels.

The treaty also merges the two foreign policy posts, uncontroversial as the role played by Benita Ferraro-Waldner as External Relations Commissioner has been eclipsed by that of Javier Solana, effectively the foreign policy chief. It shrinks the Commission, removing each country’s right to one commissioner. And it ties voting weights more closely to population, to be phased in between 2014 and 2017. All that is valuable.

But the treaty scraps national vetoes in 50 different areas, including parts of justice and home affairs; it has been wrong of its advocates to say that this is simply tidying up. It would be an exaggeration to call it the creation of a superstate, but it does transfer some powers to Brussels that were previously in national capitals. There is no point denying that – nor the uncertainty it brings. It is impossible to predict the effect as it is impossible to know what questions will eventually be put to majority vote in this way.

Most damaging, the treaty gives legal force to the Charter of Fundamental Rights, a list of supposed social and civil rights, and an enterprise of huge ambition and unclear application. For example, in declaring a right to strike, the charter may clash with national labour laws. In stipulating a right of access to preventive healthcare, it is prescribing something beyond the EU’s powers to provide.

It is inevitable that these potential clashes between the treaty and national law will be tested in the European Court of Justice courts. Famously, Britain has secured opt-outs from the parts of the charter and majority voting that appeared to pose the greatest risk of such a clash.

But it is inevitable that the opt-outs will themselves be tested in the courts. It is impossible to assume that they will hold tight. Even if the supremacy of national law looks clear – for example, in employment law – cases are bound to be brought that test that. Only after case law has accumulated will the boundaries become clear. It is that potential for legal contest – quite apart from the court verdict itself – which introduces unpredictability and expense, particularly into commercial life.

Times Recommends

• Rio Tinto four held as China prepares case
• Diplomats must keep heads down and trousers up
• When in Rome should one make like Berlusconi?