MAO Warlingham: interviews by the AAIB aren't taken under oath so the issue of a Privilege against Self-Incrimination is moot.
I don't pretend to know UK law, but in US law ANYthing you say (whether under oath or not) can be used against you in a court of law. So without special protections, any statement made to the FAA, the NTSB, or any other investigating body can be used against you. And that is why in the US there are special protections put in place prohibiting the use of such statements in a court of law.