sure his annoying fat geography teacher mate will probably be there, as well as half a dozen other people from work that i don't particularly care for

but if i keep making excuses he won't keep asking me, and he certainly won't progress to asking me out properly for dinner and snogging.

Why are you making excuses?

Go, charm him until you've monopolized him to the point where he and you ignore everyone else. Easy peasy!

what Alanna said. get gone!

the intersection of work and snogging is always problematic, but if he's snog-worthy and the work angle is managable…ask him out.

Totally^^

Also, if you ask him out, you get to have some say over whether the fat geography teacher, et al., are there too.