Jetmouse,
Written exams are marked at the flying school. You should get a quick pass/fail, and a debrief from your instructor.
The written exams have no 'cost' from the CAA/JAR, but most schools charge a fee (£10-20?) for the CFI's time in marking them.
I personally think you'd be very lucky to find sufficiently good weather in December to fit in (at least) 45 hrs in 21 days in the UK.