Filthiestfis
In answer to your original question, if someone gets hold of your bank details they could clear out your bank account in the following ways:
They could set up a standing order on your account with their own bank account as the recipient.
They could purchase goods by direct debit with your bank details quoted.
The fact that your signature on either mandate would be incorrect would not matter a jot as banks don't check most standing orders or direct debits unless they exceed a certain amount (the bank I used to work for had a limit of �5000 - nothing was checked below this amount). Technically, you would be entitled to a refund of any fraudulent standing orders and direct debits from your bank but it's the hassle involved.
Additionally, if criminals were able to marry up your bank details with your name and address you could have your identity stolen! I used to troubleshoot for victims of identity theft and trust me, you do NOT want to go there. I would recommend that people shred anything (letters etc) that has any type of personal info contained in it. Fraudsters pay people to go through your bins to locate items like that.
Ethel is quite correct in stating that cheque books contain your bank details. However, in 17 years of banking I have never seen fraud been traced back to acquiring bank details from someone's cheque book as generally cheques are written to trusted sources for legitimate transactions. That said, I no longer use one!
Hope this helps! People BEWARE!!!!!!