Colin L
High-tech low-life
Do you mean PIIGS? (Portugal, Italy, Ireland, Greece, Spain). Those countries are not causes, they are more like victims. The so-called "high debt" they have is manufactured debt due to the manner in which all EMU users are forced to operate in blanket fashion with no regard for local circumstances. Those countries actually ran austerity spending right up to the 2008 crash, whereas e.g. France was running huge deficits, yet the PIIGS countries were branded 'profligate'! The so-called "excessive" wage increases and spending is what allowed those countries to enrich mercantilist nations like Germany/Netherlands/France. Whatever any personalities may do or not do the Euro system has failure built into it. It has a central bank with no allied fiscal arm; in fact the entire conception is built around permanent separation of monetary and fiscal policy. A relic of the late 70s/early 80s. And it has barely altered in tone, though they've been forced to break their rules or crash the Euro.
It isn't diversification, but wholesale structural change required. Ideally it would be reinstatement of national currencies, free-floating. Since that's a long-term thing, it needs complete overhaul so they don't face a treasury-less central bank charged only with blunt monetary policy. The main problem is that each country is at the mercy of the ECB for clearing purposes (lending issued reserves as a central bank normally does for clearing purposes). This forces countries to actually borrow at 'market interest rates' to "temper" their spending.
The EU insisting its members move to the Euro has created a hellhole. As members try to meet the Maastricht criteria they are forced to act in ways antithetical to their economic well-being (such as e.g. Hungary). This encourages the 'creative accounting' concealing unavoidable forced debt, rather than just normal procedures for management.
Knowing that, why would the UK want to be embroiled in that system? To be sure the UK as a sovereign currency issuer can step back (as it did in the GFC) and just control the monetary/fiscal system in a direct way. Though what it did, as an EU member, was operate within similar lines: stabilising the mess and then imposing the same draconian austerity on its population as that done by the ECB. And it was entirely unnecessary, yet the UK as a member HAD to abide by dozens of agreed policies with regard to fiscal outlay. Thus it is correct to say EU membership permanently impedes a member country's ability to service its economy without destroying other members' parasitically. This is not the definition of cooperative growth or well-being.
What did the UK lose? Easy terms of trade and a right to cooperation (plus easy movement of people/capital which is another matter). That's pretty much it. Unless people think the ability to rise and profit at the expense of forcing PIIGS nations into austerity and misery is an EU benefit.
All of which rather adds to the lunacy of a Brexit given the UK had the best of all worlds, an independent currency, other carve outs and free access to the biggest free trade block in the world, all on our doorstep, and the Brexiteers still f@cked it up.