You definitely can start driving alone as soon as you've passed (as long as you're insured on the car).
I have a friend from Ireland and she only had five hours of lessons and was allowed to drive, though she can't reverse!
If you can already drive (as in have the skill), you'll need the lessons to get you into the correct habits to pass the test. If you drive for a long time, you may no longer drive like a learner and probably wouldn't pass a test! I know I wouldn't, although I am a careful driver, I do not maintain my hands in the 2 and 10 position at all times!
If you book one lesson, they'll usually assess you if you can already drive and give you an idea of how many you'll need, it shouldn't be many. Also tests often need to be booked quite far in advance as the waiting list is quite long.
If you have access to a car and a friendly Dad, you csn always practice what you have learned in your lessons, so the amount of paid for lessons will be greatly reduced. It's worthmaking sure you pass, as the tests aren't cheap either, so if you skimp on the lessons the first time, you may fail, then have to take more lessons and pay for another test. I'm sure your Dad will advise you as well. If he's not hanging on for dear life, you're probably ok!
Good luk