Voldemort spy? - flint or hint in GOF?

[Beth Currie]

No: HPFGUIDX 131899

I'm currently re-reading the first 5 books while awaiting the release of HBP
(only 2 weeks to go !!!) and have come across something in GOF which I have
never noticed before.  Forgive me if this has been discussed on here before,
I don't remember ever seeing it but there are so many messages....

I'm quoting from page 570 of the UK Bloomsbury edition.  Voldemort has just
risen and is telling the Death Eaters how he devised his plan to get at
Harry:

< "Dumbledore invoked an ancient magic, to ensure the boy's protection as
long as he is in his relations' care.  Not even I can touch him
there....then, of course, there was the Quidditch World Cup....I thought his
protection might be weaker there, away from his relations and Dumbledore,
but I was not yet strong enough to attempt kidnap in the midst of a horde of
Ministry wizards." >

What jumped out at me on this re-read was, how could Voldemort know that
Harry was going to attend the Quidditch World Cup?  Surely he should have
assumed that Harry would stay at the Dursley's for the duration of the
school holidays?  Perhaps, I wondered, he got this information from Barty
Crouch Jnr, who heard from Crouch Snr that Harry was expected in the Top
Box.  But, in chapter 35 where Crouch Jnr is given the Veritaserum, he says
that Voldemort did not make contact with him until *after* the World Cup.

So, while Voldemort was in hiding, with only Wormtail for company, how could
he have known this?  It's made me wonder whether there is an informant among
those who DID know Harry was going to the Cup - namely the Weasleys,
Dumbledore, Ron and Hermione.  Given later events and Percy's actions in
OOP, my suspicions would fall on him.  There are numerous references
throughout the books to Percy's ambitions to be Minister of Magic, and the
lengths he would go to to further his career - quote from page 463, same
edition:

<"Percy would never throw any of his family to the Dementors" said Hermione
severely.  "I don't know" said Ron.  "If he thought we were standing in the
way of his career...Percy's really ambitious you know...">

What do other people think?

Beth