The language of Brexit matters. “Transition” sounds soothing, which is why Remainers like it. “Implementation” suggests something short and sharp, which is why Theresa May, UK prime minister, likes it. “Triggering Article 50” sounds technical and unstoppable. And “soft Brexit” has a less painful ring than “hard Brexit”, which sounds faintly indecent.

Soon, another Brexit phrase will trip off every tongue: “A Canada-style free trade agreement”. This is the EU-Canada Comprehensive Economic and Trade Agreement, or Ceta — a model which David Davis, the Brexit secretary, declared last year to be “a perfectly good starting point” for discussions with the European Commission about future UK-EU trade relations. Last month, Michel Barnier, the EU’s chief negotiator, reciprocated by explaining that he knew from the moment the UK said it wanted out of the single market and the customs union, “we will have to work on a model that is closer to the agreement signed with Canada”.

Whitehall is abuzz with talk of a “Canada Plus” agreement. To the untrained ear, what’s not to like? “ Free trade” has a stout, 19th-century ring to it, redolent of Britain in its imperial heyday. Better still, Canada is a place where they speak English, love the Queen and their current premier is dashing and dynamic. So a “Canada-style” deal does the trick, restoring our fraught relationship with the EU to safer shores: the Anglosphere and our glorious past.

But such linguistic appeal is dangerously deceptive. Compared to the unfettered trade the UK now has with the EU, the Canada model — a much narrower trading arrangement — would mean erecting new barriers to business. In the words of one well-placed trade analyst this would be “the largest programme of re-regulation and re-protection” of trade since the disastrous introduction of the Smoot-Hawley tariffs in 1930. Far from being a free-trade agreement, it would be a trade restriction agreement — an act of protectionism by the UK.

If they press ahead with the Canada-style deal, the Conservatives would forfeit their claim to be a party of open markets and free trade. Their one-eyed obsession with the Anglosphere would finally bury what little remains of a commitment to liberal economics.

To explain why, compare the main features of Ceta with Britain’s current membership of the EU. For a start, Ceta largely focuses on goods, not services. Yet services are the lifeblood of the UK economy, accounting for 80 per cent of gross domestic product and a larger share of our trade than any developed economy. Even if the Brexit deal were to include stronger services provisions, it would be bound to include new restrictions damaging to the significant surplus — £17bn in 2014 — which the UK runs in its trade in services with the EU.

In the trade in goods, Ceta is not as adventurous as it seems. By the time the deal was done, tariffs had already been removed in areas where there is little mutual competition — pearls, precious metals and mineral products are Canada’s largest exports to the EU. By contrast “peak” tariffs on many agricultural products remain, and there are no provisions covering food safety and labelling requirements. There is no agreement on common or mutual recognition of standards — the key impediments to trade — just a vague commitment to greater regulatory co-operation.

UK trade with the EU is eight times larger than Canada’s. Fewer than 30 Canadian companies dominate trade with the EU, while the UK’s interdependence with the European single market involves thousands of companies, many enmeshed in complex continental supply chains. Britain is part of the warp and weft of Europe’s economic fabric. Canada is 6,000km away.

In her Florence speech, Mrs May drew attention to the deficiencies of Ceta. Yet it remains the template for Messrs Davis and Barnier. There is only a limited amount of embellishment the EU will tolerate. “Cherry picking” will not be accepted. A Canada-style agreement might sound seductive, but it would be an act of reckless protectionism that must be resisted at all costs.

The writer is the former UK deputy prime minister

Letter in response to this article:

UK is putting its weakest economic foot forward in negotiations with EU / From Dr Nicholas Dorn, London, UK

Copyright The Financial Times Limited . All rights reserved. Please don't copy articles from FT.com and redistribute by email or post to the web.