I will accept any of the following as correct answers:
Thuja (or Thuya),
Arbor-vitae or
Italian Cypress. They are all essentially the same tree, although the first answer is the correct name for it.
A number of people gave me the answer Clipped Yea, and indeed there is a website that says the hedges are made of this, but unfortunately there is no such thing as a Yea tree. Possibly the writer was going for Yew but misspelled it?
However, even if you had put Yew as the answer, I cannot find any other sites or books to back up that this is the case, whereas I can find quite a few that say Thuja or Arborvitae.
So, sorry if you came across this site and thought it was right, but I'm afraid I can't give you any marks for that answer.
On a more positive note,
JillRobinson has picked up yet another bonus point for going all Alan Titchmarsh on me and giving every possible thing I could hope to know about
Thuja Occidentalis, even if most of it was culled from Wikipedia!
So remember (especially with just five days left in the quiz and it being quite a close race for the top prizes), I'm still willing to reward knowledge with bonus points - all you've got to do is impress!