As I see it, your situation is actually already pretty good, but it's great you want to improve!
As far as the outer game goes, let's start with gym and fitness. I've seen many skinny guys packing on muscles the wrong way, doing too many isolation exercises and ending up with a muscle imbalance and a weird constitution. I'd focus on compound movements. Check out this site:
www.leangains.com it's pretty good for gaining lean muscle, it has training and diet outlined. Also check out visual impact for men, it talks about how many reps, sets etc. for different kinds of muscles (sarcoplasmic vs. myofibrillar hypertrophy). And don't worry, you can gain muscle, I'm sure, you just have to figure out what works best for you, stick to the routine and your diet. The way of eating on the first site (IF) is really good for hormonal manipulation, getting max growth hormone excretion in a natural way. Also, please don't go overboard with gaining muscle (even if you think it's impossible because you're a hard gainer). There is nothing uglier IMO than a skinny guy blowing up with a lot of sarcoplasmic muscle.
As far as style goes;
I think bad boy rock star is a great look for tall british people. I mean come on! Your accent can get you a long way in the States, you can pull off a really extravagant style, just because you're European

And it goes hand in hand with the mysterious persona. If you want to people to notice you of the bat, you'll have to get a little more extravagant and do it confidentially. Think Russell Brand style, check out what's he wearing regardless of what you think about him

He has an excellent style, and make-up. Yes, make-up. Don't shy away from eyeliner, it's amazing what it can do and no it's not gay, it's rock n roll!
http://www.google.hr/imgres?q=eyeliner+ ... 9,r:10,s:0
Do you see how it brings up his eyes? If you want girls to notice you of the bat, you have to think past your comfort zone and have some balls. I can't see your links, they're broken btw.
Now the mysterious persona. I also want to pull this off because I find that speaking too much actually breaks the sexual tension, and I'm a pretty good talker, but maybe it's doing me more harm than good. You have to talk less, not so little to look like a retard, but talk less, laugh less. You have to make strong, bold eye contact and smirk more, let the girls do the talking. Your laughter is a reward. Your attention is a reward. Don't reveal too much about you, make her work for the information.