If you want to learn theory and take the theory test with minimum expenditure, then you will have to do all the work yourself. Virtually everything you need to know is in the Highway Code (which only costs £2.75) so with a good deal of home-study and with help from experienced drivers you could learn enough to pass the test.

A growing number of driving schools are able to provide fully structured theory training - which means they will teach you everything you need to know to pass the theory test. Such training may be carried out in the car, or at the driving school's office, on a one-to-one or classroom basis. Many driving schools now offer computer based theory training; this is a highly effective method of learning the theory and is also far more enjoyable for most pupils. Whatever form the theory training takes, obviously you will have to pay for it. However, theory training often costs much less than practical training - so ask what's on offer and shop around until you find a driving school that can provide what you want.

Learning about Hazard Perception is something that all driving instructors should help you with. During your practical lessons a good instructor will constantly remind you to scan the scene in front and around you, and will point out potential hazards that you should observe as you drive. It is worth knowing that some driving schools have equipped their cars with state-of-the-art video training systems. These have a small camera in the front of the car which takes a video of your entire driving lesson. This enables the instructor to later play back and review any part of your lesson and to point out any mistakes or hazardous situations that you encountered.

By whatever method you choose to learn theory, some study at home is advisable. You need to have a copy of The Highway Code, and if you can afford it, The Official Theory Test for Cars and Motorcycles will be useful. Make sure you use the LATEST version as it's updated every year. Although this book contains all of the official questions and answers, remember it is much easier to learn by understanding the topics rather than trying to learn all the answers "parrot-fashion".
Virtually all the raw information you need for the theory test can be found in the Highway Code, but don't try and take it all in at one attempt - you will find it more easier to study one section at a time.