It's perfectly possible to pass your DVSA Theory Test without ever having driven a car.
A thorough knowledge of The Three:
The Highway Code (View)
Know Your Traffic Signs (Download)
First Aid on the Road (View)
... coupled with a good dollop of common sense will get you through the multiple choice 'written' section.
The Hazard Perception section of the Theory Test is also possible to sail; there are masses of online and DVD resources to practice, and, again, plain ol' commonsense will serve you well.
Having said that, the latter, Hazard section is very much focussed on responding to immediate conditions - you may have a hundred Hazard Perception vids to practice, but you'll find that, after a couple of shots, you know when to click the mouse for maximum score. Excellent training, but your real Theory Test vids will be unfamiliar.
This is where actual 'road time' comes in. Once you've mastered the basic car controls, and are pottering around, at even low speed, you'll encounter the unexpected: folk reversing out of driveways fast without looking; huge 4x4s pulling out in front of you from a side junction, because it's used to folk giving it room; trade vans on the way to the next job careering round a corner toward you; an, apparently, in control lad on a BMX suddenly swerving off the pavement and landing in the gutter cos he was showing off in front of the girlies.
So don't rush to get your Theory Test out of the way - use your road time to reinforce your sign/road marking/braking etc. knowledge, and your own experience of real hazards.
A bit of road time, plenty of vid practice, and a thorough knowledge of The Three. You'll comfortably sail your Theory, based on your own personal knowledge, which is always more satisfying... And you'll save thirty sheets having to take it agin!
The On Fire for Driving Team