QXC and Weather
There are many pleasures of flying in the UK, but the Autumn and winter weather is not one of them.
It can be a joy when you get a crisp clear day (or night - a rating to consider after your PPL) but depending on where in the UK you are, mist and fog are more likely.
Patience !. Your instructors are (or should be) keen for you to do well and progress. If you are having trouble getting aircraft availability, then get (politely) bolshy. People "near to finishing" are (should be) given a bit of leeway on aircraft priority - e.g. I would expect a school to help you by maybe persuading someone having a "bimble" to go an hour earlier / later so you get a clear shot.
Cancellation charges are below the belt. The place where I instruct does not charge them - equally we expect as early notification as possible - and if someone is a "no show" they had better have a good reason - i.e. If you are fair with us, we are fair with you.
Unless you can "drop everything" on a good day, then you might be waiting many weeks. You should look at the Met the night before and hopefully your work won't mind a day off at short notice. If you have a good relationship with your instructor then he may even call you and suggest that you might want to get it done today.
One good point about the winter - weekday aircraft availability at many flying schools / clubs is good. BUT very short days - you want to be away by mid morning. (If the mist has lifted !).