Fallen Eagle,
I haven't seen the advert you refer to and As far as I am aware, no UK ASU employs observers who aren't already serving police officers and the competition for the posts is strong, as one might imagine.
However, I am definitely not an authority on the subject so if you are interested in a police observer's job then I can only suggest you get along to your local air support unit and speak to them direct.
Best of luck, hope you get the job (so you will experience the TCAS problems from the other side of the fence
).