There ia couple of black biker jackets in 36 & 38 (I'm assuming that as you're 18, you're on the smaller side) around the £250 mark. But if I was you, I'd scrape the extra £50 together and go for either the seal brown Bootlegger copy: http://www.alexanderleathers.com/sale/detroit-seal-jerky.html or this Cafe Racer type: http://www.alexanderleathers.com/sale/alexander-cafe-racer-seal-goat.html
I think both are a more flexible in terms of how and where you can wear them, and classically cool as the biker jacket is, I think this pair have a bit more cache - I doubt many of your friends will have either.
That Detroit is a steal. What a nice jacket!