Hi i live in birmingham and yes this year has been a very bad growing one for all outdoor growers here. Rain and overcast through 80% of our summer roughly.....

if you cant grow in your garden with safety then a gurilla grow is your only option.with that you will need to find a spot that nobody else would go to including dogs and other animals. Putting up a shed also would be a bad idea as it would stick out obviously were as the plant will more or less blend in during the vegetatyion stage.
best advice would be to read back on other peoples diaries in this secton going back months to the start of there grows and learn from people who have done it all before and made the mistakes already.
My first grow was all learnt from this website and a couple books so get reading and get ready for next year