Will hard Brexit mean another lost decade for shares?

So Boris reckons we can secure a deal with the EU that's even better than remaining in it, does he?

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While we ponder his credibility after his earlier £350m-a-week NHS promise, it's worth considering the words of European Council president Donald Tusk. Hours after Boris revealed his unlikely vision, he simply suggested: "To all who believe in it, I propose a simple experiment. Buy a cake, eat it, and see if it is still there on the plate."

The likelihood of remaining in the single market is looking more remote by the day, as the EU insists it's incompatible with a refusal to allow free movement of people. In fact, the Telegraph was moved this week to claim that" "Privately both UK and EU officials say that means Britain will leave the single market, even if Mrs May doesn't explicitly say that."

How hard?

The question is surely just how hard our hard Brexit will be. And at the end of the two years following the invocation of Article 50, we'll have to accept whatever's on the table or fall back on potentially disastrous default WTO trading rules -- the EU is calling the shots, and we'll be the beggars at the banquet.

Former deputy prime minister Nick Clegg has suggested WTO rules would push average food tariffs to 22%. We've already seen the farcical pulling of Unilever products from Tesco's shelves in protest against prices being inflated by the pound's fall, and WTO tariffs would make things far worse.

The Times reckons that "the Treasury could lose up to £66bn a year in tax revenues under a hard Brexit, according to leaked government papers," and that trading under WTO rules could see our GDP falling by as much as 9.5% -- instead of a boost for the NHS, we'd be more likely to see higher taxes and slashed government spending.

What should investors do?

If our Brexit is hard enough to damage the passporting freedoms that our banks enjoy, it's likely to hit that sector very hard. I'm optimistic that we won't lose that very valuable arrangement and I'm keeping my Lloyds Banking Group shares. But if you have serious doubts then you might want to avoid the banks -- and anything related in the financial sector could suffer if things really are that bad.

Airlines like easyJet and Ryanair Holdings are likely to lose out too, with IATA predicting a drop in passenger numbers to 8%-9% below the likely levels that a cosy soft Brexit might leave.

But having said that, the great majority of the big companies listed on the London Stock Exchange are global and almost entirely unaffected by what goes on across the UK's borders. Look at BP and Royal Dutch Shell, for example. The UK's ex-European status is really not going to damage worldwide oil demand.

Global market

Big pharmaceuticals firms like GlaxoSmithKline and AstraZeneca, and miners like Rio Tinto, are pretty much in the same boat, with global products sold in a global marketplace. Then we have insurers like RSA Insurance, and utilities firms like National Grid, which do little or no EU trade.

A focus on global giants, on firms that won't be hit by EU tariffs, and on great long-term dividend providers -- that should see you safely through hard Brexit.

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Alan Oscroft owns shares of Lloyds Banking Group. The Motley Fool UK owns shares of and has recommended GlaxoSmithKline and Unilever. The Motley Fool UK has recommended AstraZeneca, BP, Rio Tinto, and Royal Dutch Shell. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.