sorry to hear about your problems mate,
1st off, does it make any difference that they have never heard of this problem on the 2.2i direct? who gives a sh1t what they have heard before, fact is you have bought a car that has been into vx within the first week and they have advised you that the chain sounds iffy.
imo mate i would demand that they agree that you have addressed the problem only 7 days after buying the car and you want it in writing that they will foot the bill if it goes.
if they are just happy to ingnore what you have been advised vx and just keep they're fingers crossed i would personaly drive the car through the showroom windows.
if the chain does go mate it can cause so much carnage, ok you might be covered by a warrenty but you might be without a vehicle for a few weeks whilst they source and fit a new engine...