This surprising claim, greeted by catcalls, is of course bunk. All the evidence points to our free market approach being superior to the regulated one of the continent. The second argument was also about economic efficiency. Basically it only matters in border areas where people cross to and fro to shop. Risk premia are set according to the borrower's status-AAA, junk etc.
Relative costs have, almost by definition, nothing to with monetary arrangements.
Here we had yet one more pretence from the pro-euro lobby that, like previous 'limited steps' we took, the euro is merely a technical gizmo. This is like saying of two people who refuse to marry that they must therefore wish to have no dealings with each other. Untrue in general, though possible if there is a great deal of unpleasantness.