This is very salient at this time of year but there is also an added nasty for people to watch out for.
COMET also pass all your sales information to their insurer Domestic and General WITHOUT your consent or even telling you at the point of sale. This is an offence under the Data Protection Act and is a practice that other retailers do without telling customers.
If you are asked for your name and address for the 'warranty' you should ensure that you tell them NOT to pass this information to anyone, or simply refuse to tell them the information. Ask for a VAT receipt and leave it at that - your rights are not affected.
SHARK!
For every positive action, there's an equal and opposite government plan.