Not necessary but I'd suggest a Friday night in town isn't the best time to go out for photography. There's usually lots of drunk people around, or just lots of people.
"Take my photo mate", "That's a nice camera, mind if I have it", "Can I take a picture " etc etc.
How you handle situations like this will define what sort of a night you have. It's obviously got you wound up as you've had around 5 hours sleep, yet there are times when you just have to calm situations rather than inflame them. Sometimes it's better to move on and set up elsewhere.
I've been in similar situations, the secret is to remain calm and polite and the other person usually responds similarly (eventually). Remember a bouncer/security guard on a friday night is dealing with 'troublemakers' so will have a mentality that way to start with, similar with the coppers.
To be honest, with the security guard, I'd have told him I was breaking no laws, but as he was aggressive and threatening I'd move on to keep him happy (but I'd try and get a picture of him). For the coppers, again I'd be polite and point out the rules about photography in a public place. If they suggested I move on because of possible trouble issues then again it's probably best to heed their advice. Lets face it, they've probably had a report of an aggressive photographer, upsetting people by taking photos of them and armed with a deadly tripod weapon. If you're not happy with their actions then take down their shoulder badge numbers, all officers are required to wear them (unless taped up whilst policing a demo in London

) and let them know why you're unhappy with their actions.
As for the photo, I'd up the depth of field, pick a focus point that allows for more of the shot to be in focus and set the white balance to tungsten.
Don't forget for night shots you can layer for light trails so take shorter exposures. Then you get less chance of movement blur