Hi Peter,
I'm just coming to the end of my PPl and am just waiting for the weather to get better to test.
Personally I think you need a good consistant 1-2 hours a week if not more. Any less and you will find yourself repeating yourself.
The flying of the plane only makes up about 1/5 of the PPL course, for every hour I've flown i've done a good 5-10 hours studying towards the exams, so while the weather is sh*t I would recomend you get revising and take the exams. Again, if you get all the exmas out of the way now, then when the good weather comes along you can fly rather than having to worry about studying. Especially when you consider inorder to do your 1st solo you need to have sat your Airlaw exam!
With regards to the school its self. All very well going to a small school as it might be cheaper but if it takes 15 hours longer to get your ppl than it would at a good consistant school you wouldn't actually be saving anything!
In my honest opinion, the fact your asking shows your not exactly happy at the school your at, so I would move, find a better one, probably make a world of difference