Under the Sale of Goods Act, retailers are responsible for faulty goods (that are not 'of satisfactory quality') for up to six years after you bought them. In Scotland the period is five years after something goes wrong. 'Satisfactory quality' covers various aspects that could be wrong with the goods, including whether they've lasted as long as you could reasonably expect. A 'reasonable' lifetime for different products is not defined in law and would ultimately be for a court to decide.
The Sale of Goods Act 979, amended in 1994, and the
The Sale and Supply of Goods to Consumers Regulations 2002) say that when you buy goods from a trader they must fit the description, be of satisfactory quality - which includes lasting a reasonable length of time - and be fit for their purpose. If goods aren't of satisfactory quality you're entitled to compensation, which is normally the cost of repairs. The retailer, not the manufacturer, is legally obliged to sort out a problem if the goods don't meet these requirements.
You could write your POC for the N1 simular to this one here:
Trading Standards Division - Consumer Advice - County Court Support Pack - Sample Document D