I live in an area where there are no
LGBT services or groups, neither at my school or government social/health clinics relating to
LGBT. So I feel your isolation and loneliness but I have to tell you that it isn't all that hopeless yet. There are definitely bound to be some people at your school who identify as
LGBT and you may not recognise them at first, because I didn't but around the end of last year (That was grade 10) a lot of my current friends actually turned out to be very open about sexuality and I gained the courage to approach some of the older students who were very clearly gay (ok, so I messaged them over Facebook at first but that is the beauty of social networking!) and we met at lunch, 1 gay guy and his 2 leso friends haha, they're great. Now I hope I'm not intensifying the feelings of your situation and apologies if I am.
Really what I am trying to say here is that, you should step out of your comfort zone, try and meet some new people and you are obviously keen for it with your intentions to find some groups. Unfortunately, there is the reality to the situation and it is just that, there may not be any services in your area. I am not entirely sure if you are seeking support or new friendships or both.
So I'll tell you, before all of this happened, I actually came out to my best friend and she was there for me, so even given the difference of opinion (or sexuality), your current friends can offer some support to you. Although admittedly not the same or as good as what people who share the same feelings as you do - but sometimes we just have to compromise.
But there is the Internet! It's a great way to get support, even if from anonymous people and make some interesting online friends, even if it just words on a computer screen (<- like these ones now ^^ ->) it is still better than nothing at all. In fact, a lot of my knowledge and advice (based on his past experiences) about gay relationships comes from just chatting to an american guy I met online and adding him on facebook (He's 20-25 for those wondering lol).
You will always find help in the most unlikely of places, life is strange like that.
That's all I can offer, as I'm not from the UK. :P