The county next to mine, Kent, is planning to introduce random drug testing in schools. If you don't like the fact, here's what you do. First off, you buy yourself a copy of "The Teenage Liberation Handbook: How to Quit School and Get a Real Life and Education" by Grace Llewellyn. Next, drop out. Either stop attending or maybe pop in and see the principal. Tell him that you've decided that school is a waste of time and you are going to teach yourself at home. Phone up the exam boards and organise to take your exams as an outside student. Download and print out the specifications, teachers guides and all that crap from the relevant websites (AQA, OCR or Edexcel). 
Now you need to get yourself some textbooks. Your local library will have some, but it might be easier to grab yourself some copies from Amazon's Marketplace - or new in a push. Next, find yourself some forums where you can ask questions. If you decide to go to university, you can register as an individual on the UCAS website. You may wish to consult a book called the Heap Guide to Degree Course Offers written by Brian Heap. Don't bother buying this, it changes every year - consult your local library's copy. If you want a good place to get help with your university application, go to The Student Room. If you decide to go in to higher education, you need to get student finance - try this government website for details.
Alternatively, you can take evening courses. They're just like taking ordinary courses, only you aren't surrounded by annoying people who don't want to be there. These sometimes cost a bit of money, but it's worth it - you have so much less pointless shit to deal with from idiotic asshole bureaucrats.
Most of all, do not worry. Any university worth it's salt will realise that your decision was the right one for you, and not having formal schooling can be a great positive benefit. It is something I so wish I had done. I mean, fuck it, Theodore Roosevelt got in to Harvard and then became President without darkening the door of a school (he later went on to oppose "In God We Trust" being put on the money). You have the major advantage in being able to get things done - what takes three hours in a school takes one hour at home. With the spare time, why not use it to learn about something real rather than the hoop jumping you have to do for school?
Do this, and smoke all the weed you like. And perhaps meditate upon Jefferson: "Nobody can conceive that nature ever intended to throw away a Newton upon the occupations of a crown." There's a reason why JFK said that when Jefferson dined alone, there was more wisdom than a roomful of Nobel Laureates. If you want to know my thoughts on school, look at Paine's thoughts on religion.
P.S. If you follow this advice, you owe me at least a couple of grams of the green stuff. 
