So my wheel currently looks like this:
So I don't need to bother with sprocket removal tools, all I need is to buy a single track cog. Possibly this
one (the 13t one)?
You haven't told us what kind of bike this is for or how old it is, yet! 
It's the bike with the super huge handlebar stem. You helped me out about a week ago!
It's a Halfords SUS 500 18 inch frame. The frame is small for me (I fit my Dad's 23 inch hybrid) so i've got the seat cranked all the way up, and the handlebars waaaay higher than they should be. I've since taken the stickers off to. It turned out, under all the "SUS Shockwave" stickers, that there's a silver frame in good condition. Overall, the bike is maybe 7 years old.