The world’s two biggest economies have begun negotiating a deal to create a £3.3 trillion free-trade zone – and yet my pulse isn’t racing at the prospect of the biggest trade deal in history. (Three trillion is three followed by 12 zeros, although you probably knew that already.)

It’s not that I’m indifferent to a deal that is expected to open up new opportunities for British lawyers, create jobs across two continents and boost the growth of gross domestic product (GDP) by 0.5% annually. And also help both economies combat the rampant market tiger that is China.

So what is there not to be excited about?

Well, the problem is those two economies are the EU and the US.

Superficially, everything looks rosy. Trade between them is currently worth around £393bn a year, which translates as more than £1bn a day – a good foundation upon which to build.

European Commission president Jose Manuel Barroso calls it a ‘game-changer, giving a strong boost to our economies on both sides of the Atlantic’. President Barack Obama is similarly supportive, announcing in his state of the union address the ‘launch’ of talks with the EU ‘because trade that is free and fair across the Atlantic supports millions of good-paying American jobs’.

The Law Society’s International Division is optimistic about the outcome of the talks and sees the trade deal providing new opportunities for UK lawyers. A spokesperson said: ‘Taken together, the EU and US account for nearly half of global GDP and 30% of trade flows. A comprehensive free-trade agreement (FTA) between them, which would include reciprocal market opening in goods and services, would boost investment and employment in the already open markets the two enjoy.

‘For UK law firms and lawyers, this growth would provide greater opportunities to provide services to new market entrants on both sides of the Atlantic.’

The Council of Bar and Law Societies of Europe (CCBE) is also supportive, but says it has ‘no position yet’, and will be ‘watching carefully’ as more details are published. Its Global Agreement on Trade in Services (GATS) Committee will convene soon to discuss the development, it says.

So again: what is there not to get excited about? And again I caution that we are talking here about the EU and the US.

Who’s old enough to remember the Maastricht Treaty? That was back in the days when there were just 12 member states in the EU. A draft set of treaties was drawn up in April 1991, was ready for signing in February 1992, only to be rejected by Denmark in June 1992. We all held our breath while the Danes had a second referendum in 1993, which this time was positive and the treaty was duly ratified.

There are now 27 states in the EU. What chance of achieving a quick and unanimous agreement on, for example, limiting subsidies under the common agricultural policy so as to avoid accusations – by the US – that they are protectionist and anti-competitive? Another example: it has taken decades of wrangling to get close to a single patent law covering the entire EU. Why should this FTA be any different?

On the other side of the pond, American businesses have shown little appetite for free-trade deals, lately even putting pressure on the government to implement protectionist measures to stop the domestic market from being skewed by cheaper Chinese imports.

There is also the tricky issue of car safety standards. Both the EU and the US are equally strict on this issue, except their safety standards differ from one another, so that manufacturers in the EU and US have to meet both standards if they are to export to the other.

So that’s why I don’t reach for the smelling salts when I contemplate this trade deal to end all trade deals. The negotiations will drag on for many years before they sign on the dotted line.

But it might all be irrelevant anyway. The referendum just might lead to our withdrawal from the EU – and from the prospect of a 0.5% hike in GDP every year.