But as another poster points out a page or so back, legislation is not needed to create titles. As BeatrixFan so crossly said "End of." Legislation is never needed to create a title. Nothing but letters patent are needed to create a title.
Therefore as long as it is commonly accepted - and all authorities accept it - that Camilla is legally Queen, the King may also create her a Princess in her own right and she can then use that lesser title. She is Queen in his right due to her marriage.
The sovereign is a special case here, though, because the sovereign can't hold other titles. Therefore, as you say, Camilla would have to have some title created for her in her own right as well as holding the title of Queen. I don't know if a person can be simultaneously HM and HRH, but there's no precedent that I'm aware of (as long as the HRH is a British one).
However, as we saw with the way the Duchess of Windsor was denied an HRH, sometimes these people can ignore the law if they have clever enough lawyers and can remake it to suit themselves, so maybe if they say that HM the Queen Consort can simultaneously be a Princess of the United Kingdom in her own right, they can, as the Bush administration official said about Iraq or whatever it was, create their own reality.
I still don't see any of this constituting proof, though; it's just what their spokesmen happen to be saying at the time, and as we saw from the earlier assurances quoted in the article - "Clarence House has previously insisted that the Government agreed with its view, taken from legal advice, that it was only a convention for the wife of the King to be known as Queen" - either someone doesn't know what's going on or they're misinforming us. The spokeswoman's comment
"I think traditionally that's probably the case because in all similar circumstances in the past in past royal marriages that is what has happened," said the spokeswoman.
"But I think she is not going to be referred to as Queen, she will be referred to as the Princess Consort." there's a lot of wiggle room in that parade of "I think"s.
I'm still coming back to the question of what anybody's supposed to gain by this. Even if Camilla doesn't lose her HM, which it looks as though she won't, the fact that she's known by a lesser title that's specially created for her, without precedence in 1,000 years of monarchy, is sending a message that she's somehow unworthy of the title HM Queen Camilla and that this is a morganatic marriage in fact if not in law. I don't understand why they'd want to do that. Either the Queen is the Queen or she isn't, but this is idiotic.
Also, if she does become HRH the Princess Consort, a Princess of the United Kingdom in her own right, that means she'd still be Queen Camilla in Australia, New Zealand, Canada, etc, doesn't it?