"The battle for Helm's Deep is over, the battle for Middle Earth is about to begin." So tweeted the anti-European MEP Daniel Hannam celebrating David Cameron's assault this week on the European Union, or Mordor as he would presumably call it.

Well, in his dreams. In fact, Cameron is not taking on the might of the EU. He's asking for a raft of changes designed to persuade the orcs on his backbenchers - around 60 of whom want to leave the EU - not to pull down his government.

Noises from Europe suggest that Brussels is in talking mood now that the referendum is a certainty. Even Labour has now abandoned its opposition to an in/out ballot before the end of 2017.

But Europe's problem is this: what in hell's deep does Cameron actually want?

He has been infuriatingly vague. He has spoken of ending the principle of "ever closer union" enshrined in countless EU treaties, but that's not going to happen.

Or if it is, Britain will be left in a kind of outsider status in Europe, paying contributions but without the right to shape its future. That would surely be purgatory not liberation.

He talks about ending the freedom of workers to move anywhere within the EU to find jobs. But that is never going to happen either because mobility of labour is a cardinal principle of the single market and the Union itself.

Free movement is also, like free markets themselves, a principle of Conservative economic thinking. This betrays the ugly truth that it is not really reform of institutions that Cameron is looking for - just something to halt immigration to the UK.

Realising that free movement is a non-starter he has sought to block migrants in other ways, by using the social security system. Cameron wants to deny EU citizens the rights to receive benefits like tax credits for four years after they arrive.

He also wants to end the rule whereby they can receive child benefits for children not actually living in the UK. He claims this is open to abuse, and it probably is. Though the cost is probably only a few hundred million.

But the point about all these is that he would be discriminating against EU citizens by doing so. In other European countries migrant workers have to be treated as if they were citizens of the respective country. Only Britain seems to regard this as a serious issue.

Eastern European and Baltic countries are particularly keen on free movement, which doesn't seem to make obvious sense because they end up exporting many of their skilled workers to countries like Britain where there are better paid jobs.

The reason they like it is not because they can harvest UK benefits - which anyway are far lower than in countries like Germany, Netherlands or France. It is because they tend to work extremely hard and send money home.

There is a myth that Britain is a destination for lazy European benefit tourists who want to live off the backs of British taxpayers ("just like those damn Scots"). There are a few of them it is true. But the vast majority come here to work. Half a million are here to study.

Migrant workers pay a lot more in taxes than they "receive" in benefits, health, education or any other public-expenditure provided services. UCL's Centre for Research in Migration estimates that migrants contributed £20bn to the UK economy in the decade to 2011 - a fact that only the First Minister, Nicola Sturgeon, thought worth quoting in the General Election TV debates.

Britain's "problem" is that it has a relatively fast growing economy right now by EU standards but has an ageing workforce. Britain, and in particular Scotland needs more immigration not less.

Do they displace British workers? There is some evidence that they do in certain areas of very low paid work. This is because of low pay not migrants.

It is also because of poor educational and training standards. Immigrants have higher skills and are twice as likely to have degrees than UK workers.

Let's face it. This is nothing to do with economics - it's about keeping foreigners out. Cameron has made this clear by barring EU citizens resident here from voting in the referendum.

Europe already regards Britain as a backward and faintly racist country. The next couple of years aren't going to change that.