how much do you need to pass theory test

Your pass certificate number lasts for 2 years. You must pass your driving test in that time, otherwise you’ll have to pass the theory test again.
You must book and take the full test again, even if you passed one part this time.

How much do you need to pass theory test
We provide easy to understand, fun and up-to-date official DVSA (from the people who make the test) revision content at the touch of your fingers, so you’re twice as likely to pass first time
Over 950 revision questions just like those in the real test.

Taking your theory test
A theory test is made up of two parts taken at the same time – hazard perception and multiple-choice questions.

How much do you need to pass theory test
We’ve analysed the data from the last 100,000 quiz attempts on this site. We’ve then looked at the percentage of people that got each question correct. This has revealed the most difficult theory test questions.
Because so many people use our site to test their knowledge, we have a rich history of data on each test question (over 1,000 multiple choice questions from the DVSA revision question bank). This means we can see which questions people struggle with and which ones they find easy.

References:

http://theorytestpass.com/
http://roadsafety.scot/topics/advice-for-new-drivers/learning-to-drive/your-theory-test/
http://highwaycodetest.co.uk/most-difficult-theory-test-questions/
http://www.gov.uk/theory-test/pass-mark-and-result