I have an idea which will require no law changes at all. How about the Likes of Alan Fry who so clearly dislike wealth/profits and empathise so much for the poor, stop taking advantage of any tax avoiding measures/reliefs and start donating all their excess income to the sort of causes they bang on about. Being the very senior manager he is (in charge of 1000s of by all accounts), our Mr Fry must be doing very nicely thank you and must therefore feel genuinely upset about how well off he is compared to so many here and around the globe. I therefore suggest he (and any like him who support his views) donates anything he's ever inadvertently* avoided by way of tax and any income over the UK average wage (unless he feels really charitable and wants to give more) to charity. No need to wait for a world government to be formed or even wheels within wheels to turn and new tax rules be drafted. This way he'll be setting the rest of us a wonderful example and be able to carry on his moral and political crusade free of any moral burden that he's part of the problem he spends so much of his life whingeing about. He could even post the details of what he's done here so that he might encourage others to do likewise.....
* I'm certain Mr Fry would never have deliberately avoided tax as that would seem more than a tad hypocritical.