Well under UK Law if you buy from a UK seller you have certain rights for a normal sale (meaning not an auction and possibly a few other things too) , so sale of goods, being fit for purpose, as described etc etc still apply and your rights to refunds etc etc for up to 6 years would still apply.
Enforcing those rights, whether you bought online or on the main street, however might not be as straightforward as it should be, even with a high brand name.
Two instances spring to mind in the last 20 years or so.
1/ A well known seller (example Dixons/Currys etc) sold a couple an appliance (possibly a washing machine) and it broke down after 18 months. They approached the seller for a free repair under warranty. The seller informed them, sorry no there is a 12 months guarantee with an optional 5 year warranty you could have bought at the time but decided not to. The customer was a member of "Which" and their membership included a small amount of legal services. Which drafted a letter for the customer to send to the seller quoting UK Law White Goods 6 years warranty. The seller refused so the customer took them to court. Judge said , UK Law White Goods 6 years and ordered them to repair or refund free of charge. I have little doubt that the next customer to follow this route would face a similar reluctance unless they enforced their rights.
2/ Something similar, I was asked to attend an elderly couple, their cooker grill was not working, I thought element gone, it was a little over the "warranty" period , perhaps similar to the above scenario. I informed them that probably the element had failed and advised them that if I attended and repaired it then I would of course charge them and in my opinion it should not have failed so soon. They rang me to say the manufacturer had offered a free element and they would have to get their own electrician (me) to fit it. I advised them to run this thru Trading Standards, the trading standards contacted the manufacturer on their behalf and very rapidly the manufacturer sorted out the whole repair and replacement free of charge.
Despite laws and the perceived good name of major suppliers and manufacturers you still quite often find you need to enforce your rights, small claims court is pretty easy, I`ve used it a few times (and threatened to a few more) and out of approx 20 times I have never lost.
Note - I said I have never lost, but I only won 19 times, the other one was a draw. In court the judge could not find a compelling argument either way so awarded on a 50/50 basis. Thing is, it didn`t help that I was drawn up in a feud between two parties and the other party in my case assumed I was on the opposing side of the argument against him even though I assured him that I had at least some sympathy for his point of view. Tragically the person I got the 50/50 judgement against blew himself up under mysterious circumstances, I always wondered if perhaps he had been careless mixing "strange chemicals" which perhaps were intended to blow up the property of the other party he`d assumed I sided with. I was right old long running vendetta and my personal opinion was that both of those parties had probably wronged against each other and probably each had wronged the other one too.