If it has developed the dreaded death rattle after they've replaced the timing chain and tensioner, I would expect them to replace the part AGAIN free of charge.
In theory, that should resolve it; there are a few people on their 4th or 5th part - highly frustrating I'm sure anyone would agree, but I'm fairly sure the work has always been done free of charge, regardless of warranty?
May be a different story if you'd waited 5 years before having the fix done, but since you've had your car back for the fault already, I wouldn't worry too much about £££.
Of course, it could be something more serious (without wanting to worry you!), but I'd take it back to the dealer, tell them you don't intend on spending any money, and see what they come up with!