Check the wording on your friends contract. It probably says something like 'unless you receive notification that your probationary period has completed, your probation has been extended' to cover the employer's asses. It is certainly bad practice for the employer not to have extended the probation before the deadline.
That's an interesting article, Clubman. It says "Legislation allows for a probationary term of no more than 12 months". Does anyone know what specific legislation he is referring to here? I've reviewed the Terms of Employment (Information) Act, but I can't find any reference to probationary periods in that Act.