PiB
I have never read such misinformed information written with such authority. You're not in management are you?
You cannot volunteer to work for free alongside colleagues who are being paid. Just to remind you before this discussion goes on, Yvette Cooper is a Minister. She does not make mistakes.
Ministers do not judge the law. The law courts do that. Anything said by ministers is irrelevant in determining legal outcomes except intent expressed when forumulating the original laws. In simple terms, working for free is not legal if it is always for free under the period of contract. She is not wrong, but she has no idea of the structure, and as such is irrelevant in judging BA's offer.
You display a rigid and uneducated view of the law - as HM states above, structuring through a spread of wages is possible, and furthermore the legal minimum would apply only to the period of your contract. Taking any tax year as an example, remuneration still considerably exceeds minimum wages.
Ryanair operate with many FOs who receive expenses for "training", and little in the way of salary above minimum wage.
Perhaps if BA structures it as "retraining", they could get away with paying those crew with no customer services skills for periods in excess of a year...no there's a thought...!
PiB - you don't win the argument if you shout louder...
Nuigini offered what was quite clearly an opinion. If you can't understand his/her statement as such, that is not their problem.