SkySista,
I believe it for residents and at what stage they would arrest you it's hard to know. I know of somone, who had to leave recently because she was pregnant and needed to get out before he noticed as it would have been reported (this is nothing to do with EK).
I guess officialy here it is illegal to have sex with someone unless you are married to them. You could be reported and it has happened if you are found to be cohabiting. This is generally ignored unless you've done something to pi55 off an important local.