Colin Donald shouldn't be surprised at the opposition TTIP has stirred up (Time running out for trade deal, Business, April 26).

The vaunted 0.5% rise in GDP is almost meaningless: this is 0.5% by the end of 10 years - so the total alleged gain is equivalent to 0.05% a year. What's more, alternative models (such as the one used by the UN) show a drop in GDP of 0.5% at the end of 10 years.

The gold at the end of this rainbow, then, looks illusory and, even if real, meagre. So why the rush to hand control of regulatory standards and ownership of public services to unaccountable, unelected bodies? If our standards on, say, carcinogens in food, chemicals in the workplace or GM foods, are different from those in Maine or Mississippi, that's because we have made that choice. If we have the NHS rather than America's tangle of expensive and highly unequal health services, that's because we have made that choice, as a country. TTIP would create mechanisms for overturning such choices on the grounds of commercial expediency.

The concern about supporting manufacturing is laudable, and there are real regulatory obstacles to exports. No doubt TTIP would clear some of these. But any such gains would be mere sweeties to be handed out by the negotiators, whose real objectives are quite different. The biggest goal is the opening up of huge markets in public services across Europe. The NHS is just one of many juicy targets; excluding it would still leave everything else fair game. A secondary one is the removal of inconveniences like the widespread bans on GM foods, on certain herbicides and insecticides, and other such annoying European preoccupations that obstruct American multinationals.

Here's where that rainbow really leads. Anyone who thinks TTIP is really about making life easier for knitwear manufacturers or Scottish life science companies is living in cloud-cuckoo land.

The more direct but pedestrian way to help Scottish and other European manufacturers would be to discuss, industry by industry and product category by product category, what might be acceptable standards across both the EU and the USA. That's slow and painstaking work, and often comes unstuck because some countries just can't agree. The seductive allure of TTIP is the idea that it would sweep all such difficulties away.

Much simpler to have an unelected Harmonisation Board, and if there are disagreements send them to an arbitration court consisting mainly of corporate lawyers, and unaccountable to any government. If the decision turned out to be unfavourable to Scottish knitwear or life science companies, tough. There would be no-one you could even raise objections with.

The goal of TTIP is to change, fundamentally, the way such things are decided: to remove them from the democratic arena and place them in the commercial sphere. That's why so many people are making a fuss.

Lyn Jones

Edinburgh