Maestro is Switch, it's just been renamed. I think it's also something to do with being more compatible in mainland Europe. Solo, as freak_unique correctly said is like the "baby" version of Switch or Maestro. Solo cards can only be debit cards, not credit cards and you get them if you have a low use account - basically, teenagers, students and people who earn under a certain amount (I forget how much.) They also can't be used as a cheque guaruntee card whereas Switch/Maestro can. With the arrival chip and pin most shops accept Solo cards now, but they didn't used to.
Solo cards also have a symbol on the back which looks like the Maestro symbol but is called Cirrus. I think they'll be introducing the new name soon because that's also the technology your card uses if you use a Solo card abroad.