Many thanks to everyone for reading and posting here. Today my Dell notebook was returned by courier, 12 days after it was collected. I was called in advance, it was delivered at 10 am, and Dell have just called to confirm all is well.
They replaced the hard drive, and also the keyboard, free of charge with no explanation as to why both needed replacement, or attempt to suggest it was my fault. A complete cosmetic and functionality inspection was performed (at least the boxes were ticked!).
From now on the netbook will only be used as "back up" to my Sony Vaio. I consider myself lucky the netbook was still within warranty (2 years ending this coming April).
Just for interest, Comet put me under enormous pressure to take out their own cover for the Vaio, 2 years would have cost 150 GBP. I declined, and my friends who know more than me (not difficult) tell me that was the correct decision.
If only replacing defective human body parts were so easy, but how long is our warranty supposed to last ?