Just to offer encouragement - my dad works in the car industry and thinks everyone should drive, so insisted I started lessons at 17 - I enjoyed the actual driving but the test! OMG, that fear of someone you don't know watching you!!
It reduced me to shreds and I failed miserably twice - the second time I was so nervous I mistook the accelerator for the brake and nearly killed 2 old ladies on a pedestrian crossing!
That put me off for a looong time and it wasn't until I met the OH that I began to consider taking the test again. That was all it was, considering. I ummed and aahed and then at the age of 27 my SIL (nice but bossy) bought me a book of driving lesson vouchers with someone she'd sussed out from friends' recommendations as being good with nervy drivers. She then nagged me relentlessly until I booked up a lesson.
My advice would be to do as I did, and tell the instructor just how rubbish and nervous you are, in great detail, before you've even booked the first lesson. That way they don't really expect anything of you, and my instructor even said to me in the first lesson 'oh, you're actually quite good!' which bucked me up no end.
Then, after 4 months of lessons and a few shouting matches with my instructor ('why haven't you exited the junction yet?' 'why are you going so slowly?' BECAUSE I'M SCARED, GODDAMMIT!!) I passed my test. With the aid of a bucketful of Kalms.... I think I scared the examiner, I nearly kissed him when he told me!
And then I had several months of driving like a tortoise in a car festooned with 'P' plates, but practise is a great confidence booster - in the end, what got me going was driving to my stable yard - it took 40 mins by the side roads and only 20 on the North Circular, so I screwed up my courage and went for it - now I'm a total girlracer, which is probably just as bad as being a nervous nelly!
So go for it - you really won't regret it!