"And what kind of "IT worker" can't even figure out how to wipe a hard disk?"
And regarding "it has his National Insurance number on it", in the same paragraph the article refers to "personal files". Such personal files could include scans of his passport/driving license, list of passwords used in several sites, bank account data, list of favourite porn sites, "naughty pictures" pictures of his wife, "naughty pictures" of his sister in law or any other thing you can think of that could cause him to have his identity stolen, suffer emotional stress, suffer a traumatic divorce or...
In normal conditions, he could have talked to a friendly Harrods IT guy, asked him to erase or recover the files and fix the issue easily and legally. Unless, of course, the working environment was very "toxic", or the IT support was outsourced to some Third or Second World country where Privacy Protection laws are not all they should be. If any of this was the case, asking the Harrods IT bod would be like walking nude at 3 A.M. in a marginal neighbourhood with a big bullseye painted in the arse*.
*:Can't end well! 8^)