Hi Jetmouse
I'm afraid I've some sympathy with some of the other responses, if you're balking at spending £20 and some travelling time (some if which might be wasted) then GA might not be for you. If its one thing you can count on then it is that you will spend more time and money than you ever planned to when learning, and indeed when you do get your license.
On a more constructive note, I guess you've got 2 options:
1. Become sh*t hot at Meteorology...don't forget you will have to make this call for yourself one day so you'd best get into the habit of being able to assess the weather from day 1. Note that wx requirements for training will be different than 'normal' flying, so have a chat with an instructor so that he/she can lay down some guidelines for you to work with. If all else fails just call the school in advance of time for their advice
2. Got to the US...3 weeks is going at it something but it can be done
Good Luck