Money has gone into my account in error can the bank take it back without my permission?

Yes, they absolutely without a doubt can take it back. Just because they erred and put it in the wrong account (yours) doesn't not mean you are entitled to it. If your money went into someone elses account due to bank error, wouldn't you want the bank to take it back and give it to you? If you notice(d) it before they did, wouldn't you want to be honest and call them to tell them?