The theory test is one test, split into two parts: a multiple-choice test, and a hazard perception test. You'll need to take them together and pass both parts at the same time.
To pass the first test you must correctly answer 43 or more questions out of 50 within 57 minutes.
This 20-minute test is to ensure that you are able to scan the road, and recognise potentially dangerous driving situations. It contains a series of 14 one-minute video clips showing potential road hazards.
You have to identify 15 developing hazards (one clip has two hazards). The faster you identify them, the higher you score - each hazard has a maximum of 5 points.
To pass, you need to score at least 44 out of 75. You can't repeat any of the clips – the idea is that on the road you don't get a second chance with hazards.
The fee for the test is £23. To cancel you must give three clear working days' notice or you'll lose your fee.
You'll get your pass certificate, which lasts two years. This means you have a two-year period in which to take and pass your practical test. If you don't do it within this period you'll have to take the theory and hazard tests again.
Study some more, then take the test again. Another common reason for failing is forgetting the rules of the road.