If consent is required but not signified, a bill may make no further progress through parliament. If a bill is mistakenly allowed to progress even though the required consent was not signified and the error is discovered before royal assent has been given, the proceedings may later be declared void.[18] Where a bill requires the consent of the Prince and Steward of Scotland or the Duke of Rothesay, the Scottish parliament cannot debate any question whether the bill be passed or approved unless such consent to those provisions has been signified by a member of the Scottish executive.[2] Once a bill has passed parliament and received royal assent, it is regarded as legally valid by the courts, regardless of any deficiency in parliamentary procedure, in accordance with the usual principles of parliamentary privilege.[3]