Is England not pretty liberal about weed usage? Just roll up a joint (you might want to practice with tobacco first), head to the park and smoke it like a cigarette. If you see a cop just casually put it out.
Also, check out the
prices thread for your area, there is a search function for every thread. Just from a quick search it looks like 20 pounds will get you 1/8 of an ounce (or 3.5 grams), which can last a pot newbie a fair amount of time.
Glad to have you on board man, and don't feel stupid about asking questions around here.