Let me know exactly where you are in Essex, I know the area and could advise you if you're around Guildford...
I would say go for a beginner's class (let the teacher know if you are... that will helps placing you in the right class for you).
There is no real advantage at this stage to go to a private class, because this is more to 'remedy' a problem that is there or work on something specific, but because you are starting, I would really emphasise the importance of going to a class with others. I know it's daunting at first, but it's truly the best way to learn from everyone's mistakes. I'm sure you won't be the only beginner there, and you can then make friends who are also 'in your shoes'...
Be bold, make that call.

(You may want to take a 'test' class.. Normally, the first trial class is free, so you wouldn't have a problem checking various schools and teachers' personalities to fit your needs best).
At your age, you may not be able to access adults beginners classes yet, but maybe a teenagers beg. class could suit you... Speak with teachers, they'll know best! :p