You can do all the exams without even seeing a Cessna.
All the schools round my way will let you come in, pay your £20 and take the exam. I am learning at one school, and have taken my exams at 2 others just because they are near work, and I can pop out at lunch and do a quick exam.
Get some evidence that you have taken and passed the exams, your FTO will almost certainly require the LAW exam before they let you solo, and all the rest before they let you do the skills tests.
Dont forget the RT theory and practical exam.