It shouldn't be a problem because it only reveals the same details as those contained on a cheque. However, as was pointed out, Clarkson did get stung. I believe this was probably done by a mischievous person who worked in the banking system itself because by just knowing the sort code and account number, you should only be able to pay money in to the account. Also, with Clarkson, it should be noted that the unauthorised transfer was made to a third party - a charity. If the transferrer had taken money for themself, it would have been traced. Mind you, I suppose there's nothing to stop a bank worker setting up a dummy account to receive and just withdraw by ATM. I would hope it's more secure than that but after reading about some bankingf glitches, I do sometimes wonder.
I am in the process of converting as many customers to bank transfer as possible. I'm doing it at the same time as increasing prices as a sweetener. Basically putting prices up by a pound doesn't seem so bad if they are offered the chance to save 30 - 40p on postage.