As others have said, a Warranty has a fixed time and that is it. That the product is unusable for a part of the period doesn't mean the warranty is extended, pro-rata.
Worse, many car warranties clearly state that any part fitted under warranty is only warranted until the end of the original warranty, not for 12 months as one might expect.
As of YESTERDAY the consumer rights act in the UK has changed.
2015 Consumer Rights Act This link explains what it means as far as cars are concerned:
New Rights The key change is that there is a 30 day right to reject. Be interesting to see how this works through the motor trade.
