I mean, that Astra, surely the life time warranty has major T&C's that you have to follow stringently.
Not really
The major condition is that the lifetime warranty only lasts for the duration of the 1st owner. Once its sold or traded in the lifetime warranty has gone.
Vauxhall obviously did their research and found out that vauxhall 1st owners on average sell their cars on or before the 5th year. So it may look massively expensive, but in fact is no more expensive to them on balance than the other manufacturers 5 year warranties.
Except vauxhall call theirs "lifetime" and get a massive PR spin because of it. They will make a loss on some owners who own the cars for donkeys years, but make it back on those who trade it in after 18 months because then the warranty will only last 3 years from manufacture for the 2nd owner.