Ready to book driving test?

[Frecklesandspecs]

I've been having lessons for about 6 months and just wondered if the driving instructor usually tells you when they think you are ready to book the test or if you should ask?
How can I know how far off I am?
What things should I be able to do beforehand?
I'm driving pretty much without any help. Parking, 3 point turns and reversing ect....
I'm doing automatic so it hasn't taken as long to learn (was rubbish at manual!) and I feel fairly confident but I know it can take a few months to book the test too.
How did you know?

After 6 months I'd expect to have passed my test, especially in an automatic.

My instructor told me when he thought i needed to book it - i would ask him though how far off he thinks you are
Key things you need to be able to do:
turn in the road
parallel park
reverse around a corner
emergency stop

have a really good knowledge of the test routes your test centre uses - your instructor should know these
know the essential bits under the bonnet (engine oil, screenwash, dip stick)
know where you find tyre pressures

Do I need to have passed theory before I book it?
(I know I need it to actually take it)

You need to show your theory test pass certificate at your practical test.

Do your theory asap - you can't book your practical until you've passed it and it took my 4 weeks to get a theory slot then 8 weeks to get a practical. If your instructor knows you haven't done your theory then they won't tell you to book your practical so book it now!