http://www.theguardian.com/football/201 ... mands-hmrc

Unless I've missed something, how can the law change be retroactively legal?

Technically the law hasn't been changed. What has changed is how the law is interpreted by HMRC and they are allowed to go after tax that should have been paid under the current interpretation, even if it didn't need to in the previous interpretation, I think for several years. This just illustrates how utterly ludicrous UK tax laws are.

I have limited sympathy to be honest because they were all very rich men and could probably have afforded not to avoid the tax and still been very rich men. But HMRCs ability to change the rules as, when and how it feels like it is demonstrably unfair and wrong.

While I'd hardly say my heart bleeds this sound like bad financial advice, all be it with a massive financial impact.
Maybe I'm being massively unfair but not many, if any, footballers strike me a financial geniuses so they have to rely on the people they employ to advise them well and handle their affairs properly. I suspect in the majority of these cases they've been let down badly.

I'm not sure its fair to say HMRC changed its interpretation of the rules. The law was changed by the government in 2013 to allow them to do this sort of thing. They are just using their new powers the way they are meant to.
I do however think it's a bit off for hmrc to be able to demand payment up front while the cases are still going through the courts.