robovski:
It's safe for the seller but I never use it as a buyer as there is virtually no way to get your money back and no gaurentee offered by eBay. As said above, the worst they can do to you with just name and account details is set up a direct debit or create fraudulent cheques (way unusual that). They would need personal details as well to begin to do real damage to your account.
If you have a Halifax or Bank of Scotland account, and they do too an internal transfer could be arranged on just the roll number of your account. You wouldn't need to give up the sort code and account number then but they would need your name to confirm the recipient.
This is the best advice. If you pay using BT then the seller can just keep whatever you bought and there will be nothing you can do about it. Ebay, paypal and the banks will just say "tough!".