Thanks all
You're right Jamie, I do think the treadmill is a bit flattering on the times - although i've done some 5k's outside and whilst certainly tougher, I found it good going and faired quite well.
I think I need to find some local races and get involved. And you're also right about the 4 / 5 milers after work, all done pretty much at roughly the same pace (not flat out, but not far off) I did pick up an IT band injury a few months back, but since then (touch wood) i've been ok.
I'll take the advice and do a slow long run, and a few quick sessions and see if I can improve more !!
Thanks again, lets see how I get on tomorrow morning.