There are very few questions that you are obliged to answer by law. Normally, you are required to give your name and address and produce evidence of the same if requested by the police, as long as they have certain beliefs about you.
Commonly, any person has to truthfully state who the driver of a motor vehicle was at any time. It is an offence not to answer those questions truthfully. However, you do not commit an offence if you simply don't know.
There are of course other discreet occasions where you may be lawfully required to answer questions. You should always seek the advice of a solicitor.
There are many occasions where a lawyer will advise you not to answer any questions other than to give your name and address. This is often the best course for you unless you are compelled to answer questions. Despite beliefs to the contrary, this advice is not just given to protect the 'guilty'.
In our vast experience, we do not in this day and age have the faith that your answers will be treated impartially. We have had many cases where the investigators have not properly investigated the matter and only looked to discredit what you say. It is not always just because they don't believe you. Police are understaffed and under-resourced and the reality is that your answers do not receive the due attention they deserve.
Secondly, it is our experience that the police now lack authority in many cases to adjudicate upon matters and prefer to leave it to the court to decide.
Lastly, in cases where a victim exists, we have had occasions where your answers are put to the 'victim' only to find a change of story results.