AT A GLANCE: legalities and limitations

Is Brussels trying to make Britain remove passport controls?

Yes. Although the Commission is not taking any specific action at the moment, legislation is likely this year. But it won't necessarily succeed.

Why is legislation on the cards?

Because the single market, which we agreed to in 1985, is supposed to remove all borders between countries, creating a frontier-free Europe. The Single Act was supposed to lead to the freedom of movement of goods, services, capital, and - crucially - people.

The key section of European law, Article 7a of the EU treaty, says so. That bit of the treaty has been law for nearly a decade. It is supposed to allow free movement around the Union for all EU citizens - though not (at the moment) for immigrants from outside the EU.

So has Britain signed away the right to border controls?

Not as far as the Government is concerned. When the heads of government agreed that bit of the treaty in 1985, they (including Mrs Thatcher) added a rider. It said that the agreement would not affect a government's right to control immigrants from countries outside the EU. This "general declaration" was tacked on to the end of the Single European Act. It is not an opt- out, because it applies to everyone and because it is interpreting the treaty, not saying that the treaty doesn't have to be obeyed.

Why is Charles Wardle so worked up then?

Because he thinks the "general declaration" is not worth the paper it's written on. The European Commission certainly believes it does not change the treaty's requirement that internal border controls should cease, for immigrants, as well as EU citizens. Mr Wardle wanted the general declaration turned into a cast-iron legal guarantee next year, when the EU rewrites its treaties. John Major says it isn't necessary, because the declaration holds good.

Who's right?

Both, probably. The "general declaration" appears to have little legal value; even some British officials admit that there is a big legal question mark hanging over it. On the other hand, if the Commission introduces legislation this year to take away border controls, as is likely, Britain could veto it - and might get support from some other states.

So there's no problem?

Not yet. The twist is that the European Parliament - which wants border controls to go - has taken legal action to make the Commission act. There could even be a legal case in the European Court of Justice to make Britain comply with the no-border rules. But it isn't certain that the court could rule on a case like this, and it isn't certain that it would decide against Britain even if it did, and the whole process would take years, by which time there could be a political fix.