Further to Ethel's answer, you'll also probably need quite a bit of money in the bank. Barristers are self-employed and they often don't get paid for many months after the resolution of a case (which itself may have lasted many months). That means that barristers frequently have hardly any income for the first year of their career. However, during that time, they've not only got to meet the normal living expenses that everyone has but also pay substantial fees to the chambers that they work out of (for such things as rent, secretarial services and payments to the clerks). I've seen figures suggesting that a barrister needs between �50,000 and �100,000 in the bank before he/she can start work.
However, you should watch out for an answer to your question from Barmaid. She'll be able to tell you far more, because she's a barrister (appearing in the civil courts).
Further career information can be found here:
http://careersadvice.direct.gov.uk/helpwithyou rcareer/jobprofiles/profiles/profile625/
Chris