Sometimes, not always, only if your rights have been breached. And it is only 6 years to pursue a claim, therefore you'd ultimately have to take them to court and prove it was defective when sold to you. Same as the second year of the EU warranty, you have to prove it was defective at the point of sale.
I think you would be very unlucky if a small claims judge did not agree that a TV should last for more than 18 months.
In the UK, technically, the burden of proof is on the buyer after 6 months since the purchase. Fortunately most manufacturers offer 1 or 2 year warranties. In this case, it is only 1 year.
You are correct about the 12+ month burden of proof in the EU though. It prompted many manufacturers to go from 12 to 24 month warranties because sellers did want the potential liability in the second year since sale. I noticed that post BREXIT, some manufacturers continued to offer EU citizens 24 months but only 12 to UK citizens.
When it comes down to it, IMO, a solid state device, such as a LED TV, should last far in excess of 2 years.
I would suggest that the OP use social media, such as Twitter, to ask Argos if it is happy with TVs that they import failing after 18 months. If no joy, then contact the owner of Argos, Sainsbury, via twitter.
If still no joy. Lodge a case with the small claims court. It will cost Argos more to defend themselves than to replace the TV.
If the TV was purchased on a credit card, section 75 may, or may not apply. It may be possible to convince the credit card company that the TV was not of merchantable quality.