What is the standard of care a lawyer owes to a client who retains him?

The law that governs the professional standard of care that a lawyer owes to a client who retains him is well settled. While there has been an ongoing debate on whether an action brought by a client alleging breach of the standard of care by a lawyer is founded in contract or tort, everyone seems to agree that the standard of care is the same. Thus it makes little practical difference whether the lawyer was negligent in serving his client thus occasioning a breach of contract or that he was negligent in the tortious sense - the result will be the same. In this case, there is no question that the defendant was retained to act for the plaintiffs and his duty of care therefore becomes the generally accepted standard of the ordinary competent and diligent solicitor. In Groom v. Crocker, [1939] 1 K.B. 194; 108 L.J.K.B. 296, it was put this way: Lawyers are bound to exercise a reasonable degree of care, skill and knowledge in all legal business they undertake. Their liability arises out of contract. The standard of care and skill which can be demanded from a lawyer is that of a reasonably competent and diligent solicitor. It is not enough to prove that the lawyer has made an error of judgment or shown ignorance of some particular part of the law; it must be shown that the error or ignorance was such that an ordinarily competent lawyer would not have made or shown it.