It warms my cockles to see you reading the Economist Joe, but nowhere in that article does it say what you think it does. It points to the five economic tests that were put in place to gauge the merits of joining the Euro, and if those tests were passed, and therefore the Treasury deemed it in the national interest to join, then we would join (providing a referendum agreed).
In total, I believe the analysis by the Treasury ran to some 2,000 pages. As an example of evidence based decision making, it seems infinitely better than deciding based upon whatever can be scrawled on the side of a bus