So if Robson/Rae win the doubles rubber does that mean were through to the next round
Not quite, we would lose to Turkey if they beat Portugal and us, and Portugal beat Latvia. And we would be in a 3 way tie for 1st if Turkey win both games and Latvia beat Portugal (which would be decided by sets won, so we currently have the advantage of having won every set so far).
Oh heck, that's complicated. Is it a mini league thing with only the top team going through?
So if Robson/Rae win the doubles rubber does that mean were through to the next round
Not quite, we would lose to Turkey if they beat Portugal and us, and Portugal beat Latvia. And we would be in a 3 way tie for 1st if Turkey win both games and Latvia beat Portugal (which would be decided by sets won, so we currently have the advantage of having won every set so far).
Oh heck, that's complicated. Is it a mini league thing with only the top team going through?
Yes, it's complicated - rahter like the ATP finals. Round-robin groups, with rules for deciding who goes through if teams are tied.
Full explanation in the FED cup rulebook http://www.fedcup.com/media/247912/247912.pdf see appendix A clause 11 (on page 34, which is actually the 40th page of the pdf)