Common problem with the Zafira, this bloke can do it without taking the head off, he quoted £120 for the first one, then £60 for the last 3, if you need all three doing. Although if you're doing them, you may as well do all 4
https://www.threadworx.co.uk/
But as you say, if you've got to do the camchain, then the heads got to be taken off.