Indeed. I was curious about the legality of it all, as bigger organisations usually have an arbiter of sorts to draw the winners (I work for a charity and we run several raffles a year), but I can't find much information. There doesn't seem to be any issue with Andy buying tickets and I can't imagine anyone begrudging him an opportunity to win after putting in all of this effort. I think in the interest of fairness the person who draws the tickets should not be someone who has purchased any, but I can't find anything restricting who can actually do this. I did find out a couple of things though: it's illegal to spend more than £500 on prizes (irrelevant, as all prizes are being donated) and it's illegal to spend more than £100 of the raffle ticket purchases on costs of the event/printing tickets/etc. I also don't see that being an issue as Andy has managed to get the cost of the hall organised through sponsorships, and if any other costs exceeded £100 I'm sure everyone would happily contribute.
Re Totally Dubbed's request, it's also unfortunately illegal to sell tickets remotely. The only people who can buy tickets have to be present at the event and the draw has to happen, with all prizes being handed out, by the end of the event. You need a license from the local authority to be able to sell tickets remotely (or offer a cash prize), which I don't think would be possible for this.
Hopefully this is helpful!