There is a risk that one of the euro zone's 17 member states could leave the single currency bloc, Bank of England policymaker David Miles said in an interview broadcast on ITV late on Wednesday.

I don't think any of us can feel confident one way or another about whether all the countries that are currently in the euro zone will still be in it, he said.

Earlier on Wednesday, an unsuccessful German bond sale sparked fears that Europe's debt crisis was starting to threaten even Berlin, with the leaders of the euro zone's two biggest economies still at odds over a longer-term structural solution.

(Reporting by Michelle Martin; Editing by Richard Borsuk)