You know, I always wondered why everyone was so ahnospraydyeskthxbai! The only place I can buy that stuff is from a beauty supply store, so I haven't had the problem with it getting all over things. Actually, I can get them at Wal-Mart right now because it's Halloween, but I did that one year and it was pretty bad. I got it 'cause it was cheaper than the stuff at Sally Beauty Supply - and now I know that there's a reason for that!
Anyway, this is the stuff I normally get:
Streaks 'N Tips Temporary Highlight Spray
I don't know if you can find it in the UK though. I like it because it shouldn't stain your hair like most black dyes would, and it is truly
temporary, not like a temporary rinse which would take multiple washings to get out of your hair. Just brush your hair before you wash it and it comes out like a charm.
However, if you do decide to go this route, do not
do it inside and do not
do it while wearing your costume. I used to do it in my bathroom, and I would think it didn't make a mess, but then later when I'd wipe down my counter top and sink it would turn the paper towel the color that I'd sprayed my hair with. It comes off my counter and sink pretty easily, but I'd hate it if it ruined anything in your home, so better not risk it. You probably already know why I said don't wear your costume when you do it, so I won't bore you by explaining that part. Finally, I would recommend that you wear some kind of face mask when you do this. Spray dying my hair tends to make my nose run a little, and when I blow my nose (sorry if this grosses you out) my nasal mucus is the same color as the spray dye.
I probably just added another reason to the "Why You Should Not Use Spray Dye" peoples' list, lol. But honestly, for about $5.00 I can cover my shoulder length hair in a different color. Now, for Halloween or something where people don't really care how amazing my costume is, especially if I'm only going to wear it once, I think $5.00 is a way better investment than spending $25.00 or more on a nice wig.