Had he paid the £56 he would have had no worries. You did say "he was pleased with the laptop", and now you or your brother want some extra out of warranty work done for free.
If your house as an household and accidental insurance cover, then you may have grounds on making a claim via that.
Regarding the fire and safety risk, I would take this up will Dell, as it would appear as though this fire risk is not unknown (another thread in Speaker's Corner).
At the end of the day, Dell are there to sell things, and not provide free service, that's what business is all about. Telling people not to buy, on an after event, is not the way to go about things.Deal with this matter politely, and perhaps Dell will come to you and your brothers aid.