Well, as someone who has undergone the teen party scene (and still is), I have a little advice.
At first, I was kinda paranoid like you. I didn't wanna get jacked up for fear of doing stupid things. So, I picked up on a little strategy that I learned from my AP Bio teacher (a crazy dude indeed). Now this kinda kills multiple birds with one stone, assuming your situation permits it.
Throughout the party, if you can, alternate every alcoholic beverage with a drink of water. For example, one beer, then one water, then one beer, then one water, etc... This not only keeps you hydrated (which is important since alcohol dehydrates you, but this significantly lessens the effects of your hangover), but it also keeps you with a drink in your hand, keeping your pride or whatever in tact. It also makes you piss way more, lessening the effects of the alcohol (yes, jackal, holding it in is bad).
I don't know if you'll be in a similar environment, but when I did this every party had those little red plastic cups. It was nice cause I could use the same type of cup for the water and then alcohol. No one knew the difference. The point of drinking is to feel the effects enough to have a good time. If you fall down drunk, you aren't having fun, so just drink enough to feel "good." Don't feel pressured into getting hammered.
Now, I'm a big fella (6'3" and about 245 lbs), and after a while I found that I could hold me alcohol pretty well, and eased up on the one beer, one water thing. But, this is your first time (you virgin ;P), and you shouldn't be heavily drinking. This might not be the best place to drink for the first time. It sounds like it is focused on hardcore drinking. If you can get away with my little strategy, then go for it. If not, then live to drink another day. Hopefully an opportunity can come by that allows you to test your limits for the first time.
I hoped this helped somewhat. I feel like I really understand the situation you are in, as I was there not so long ago. I see many parallels like parents (I have a similar type, from what it sounds like), and having friends that had already benn drinkers, and needing a way to get home (the one difference being that I am in the US, not the UK). If you have any more questions though, feel free to ask. I have plenty more advice. :)