And indeed, in 2007 someone appealed a camera speeding ticket all the way to the European Court of Human Rights, saying that this system violates the right to remain silent!
Unfortunately, the court rejected the argument. "On the one hand, it was self-evident that it was incompatible with the immunities to base a conviction solely or mainly on the accused's silence or on a refusal to answer questions or to give evidence himself. On the other hand, the immunities could and should not prevent the accused's silence from being taken into account in situations which clearly called for an explanation. The conclusion was that the 'right to remain silent' was not absolute"
That - to my understanding - is backwards. The power of the monarch is subordinated under Parliament. Parliamentary sovereignty is inherent, not derived from the crown.
HMG - not parliament - exercises the royal prerogative (those powers retained by the Crown) on behalf of the monarch.
In reality, yes. But technically the monarch can veto any Act of Parliament and appoint anyone as PM, though this would last about a day until there was a 'revolution' and the monarch was formally stripped of power.
It is not clear to me that any of the constitutional documents in the UK enshrine a right to silence. The Right to Silence in the U.K. is generally built up on common law, not statue. Every essay I have ever found on this topic refers to the right to silence in the UK as predicated on common law, not on statute, let alone on a critical constitutional document that would require explicit repeal.
So yes, Parliament cannot implicitly repeal some documents. But I don't think that the Right to Silence is in any of those. Of course, citations to the contrary would be welcome!
EDIT: And in fact the law has been challenged, all the way to the ECHR. The challenge failed: https://www.theguardian.com/uk/2007/jun/29/transport.eu
In this case, there is an Act of Parliament (Section 172 of the Road Traffic Act 1988, as amended by Section 21 of the Road Traffic Act 1991) that makes it an offence to withhold this information. That is the end of the story: Parliament has said it, therefore it is so.
(Note that in the U.K. there is currently a way out: the ECHR. I don't think they cover the right to not self-incriminate, but if they do that would be a possible challenge.)
Remember: in the U.K., Parliament governs by wielding the power of the monarch. That power is formally unbounded and absolute.