Those wanting the UK to leave the European Union have won the referendum battle but it is still far from certain that they will win the Brexit war. The task before the UK is huge, and it may be that Article 50 is never invoked. If there is a Brexit, or a radical new basis for UK membership, this may have to be by an entirely new treaty.

One thing is plain: Brexit cannot be quietly abandoned. The Leave win was narrow but decisive and Remain was emphatically defeated. No political fact is so stark than that of the EU referendum result. It cannot be forgotten or wished away. Most UK citizens who voted in a referendum set up just to ask the question said they want the UK out. That was in the face of expensive government propaganda.

This vote must mean the issue of the UK’s relationship with the EU, which has dogged British politics for more than 40 years, has been decided. If so, no future Thatcher will need to face down a Jacques Delors, no future Major will have to contend with Maastricht rebels, and no future Blair and Brown will need to find excuses for the UK not to join the euro. The matter of the EU seems to have been resolved, to the extent that it was capable of resolution.

But there is a serious problem. Making something happen is not the same thing as merely wishing for it. It may be near-impossible for the UK to leave the EU, at least in the next few years. And just as the brutal fact that the British people voted to leave the EU cannot be ignored, the fact that leaving the EU may not be possible cannot be ignored either.

So extensive are the EU ties which bind the UK that they take at least a political generation to untangle. Gus O’Donnell, the former head of the UK civil service, has pointed out that it took Greenland, with a population less than Croydon and with only the issue of fish, three years to leave the old EEC. And in the Eighties the EEC was a far less complicated entity than the modern EU.

Thousands of UK laws — nobody knows exactly how many — are based on EU law. Many of these laws only have effect because of the European Communities Act, which would need repeal or substantial amendment. Some of the laws have effect without any UK-implementing measure.

Millions of pounds of funding for agriculture, regional development and scientific research comes from the EU. Almost every policy area you can think of, from medicines to television, has a EU component and many UK public bodies depend daily on EU institutions providing information.

Each policy area needs to be examined so the Government will put appropriate measures in place. All this will have to be done on top of what the Government will be doing anyway running the country, in a period of budget cuts and spending freezes, and with a civil service that is 20 per cent smaller than in 2010.

Cutting the EU out of UK domestic law and policy is not some discrete surgical operation. It will be the political and legal equivalent of separating conjoined twins. And this is only the start of the problem. One special feature of the EU is the enforceable rights it gives citizens and companies. These so-called “acquired rights” are, in principle, enforceable by any EU citizen or company wherever they are in the EU. The most notable of these rights is that of free movement but others deal with the other “freedoms” of capital, goods and service provision. Brexit may mean the rights of UK citizens and companies in the EU face being extinguished, as do the rights of EU citizens and firms in the UK. The Government already seems confused about what to do about this, and if it puts a foot wrong then substantial litigation is a near-certainty.

But the Government does not know what sort of Brexit it wants. The referendum only asked about membership of the EU. It did not propose any particular model.

Some urge that the UK stays a member of the “single market” which means the UK accepting EU law and policy without having a role in the making of it. Others propose a customs union, which would mean that the UK would have to accept tariffs set by the EU. Each compromise model means the UK will lose some control. This is presumably not what people voted for in the referendum.

A minority of Brexiteers are clamouring for the quick break of a “Hard Brexit”: in effect, tearing the conjoined twins apart in one hefty pull. This will not happen, and for good reason.

The problem with this is not only all the legal and policy complications, it will propel the UK into a world of tariffs and other barriers to trade. The UK’s agriculture, manufacturing and services sectors would be critically endangered overnight. It cannot even be taken for granted that we would immediately get membership status at the World Trade Organisation.

Any balanced trade agreements with the rest of the world will take time. The Chinese and Australians took 10 years to complete their recent deal. Unless the UK accepts a series of one-sided deals then that is about how long it will take the UK to conclude agreements with other major economies.

Time is not the only problem with trade deals. In the modern world, they are rarely about tariffs and quotas but cover “non-tariff barriers” such as competition policy, consumer rights, access to public procurement, and intellectual property protections. In other words, domestic policies. The most notorious example of such wide-ranging agreements is the US-EU Transatlantic Trade and Investment Partnership, but this is not the only one.

A post-Brexit UK may be less about “taking back control” and more about giving it away in return for a trade deal. And, in any case, no major economy will want to do a deal with the UK until they see what form Brexit takes.

There is currently litigation about whether an Act of Parliament is needed to commence the Article 50 exit process. There is also uncertainty as to what will happen if the Scots and Northern Irish remain opposed: the referendum question was about the UK leaving the EU and not just England and Wales. But these major constitutional problems may be less important to whether there is a Brexit than the immense practical difficulties of making Brexit work.

The referendum may have given irresistible political force to the Leave side but membership of the EU may prove an unmoveable object. There is a contradiction, and nobody can predict how this contradiction can be resolved.

David Allen Green is a law and policy commentator and a solicitor at Preiskel & Co LLP.