The guarantee may have expired but that's not the end of your rights.
There's additional cover under European legislation to do with a "reasonable lifetime" of a product. In other words you could expect a quality major brand TV to last say 6 years, and maybe less for a cheap supermarket brand. But you could still say that 3-4 years is a reasonable life time that you could expect the set to work without fault. Certainly just a year or 18 months is unreasonable.
Your rights outside of the manufacturers guarantee period are different. For example, you can't expect a free of charge repair unless you can prove some sort of manufacturing defect existed. Nor could you expect a full refund or a no-cost replacement. What you might be entitled to though a a reduced cost repair or a partial refund based on the length of time you have owned it.
Supermarkets are notoriously bad at aftersales repair support. The people at customer service haven't a clue about the goods they sell. Nor is a company like Tesco geared up to provide repairs. That's part of how they achieve lower prices. You thought you were getting a bargain. But in reality you were just deferring some of the cost on a gamble that the TV wouldn't go wrong. Sadly this time the gamble didn't pay off. Personally I think this is a bigger rip-off than overpriced HDMI cables. It's a national scandal.

It's all the more galling because in this case the Technika brand is owned by Tesco. The firm is happy to take the extra profit it gets buying direct from the factory on a no-returns basis. But it is then ignoring its responsibilities for support that should be paid for from that extra profit.
The fact that Tesco can't offer a repair service might actually work in your favour. They are more likely to offer a partial refund or a replacement TV with you making a contribution to the difference in cost. If they offer you a refund then take the money and
RUN!!! Don't buy another cheap crappy brand TV again. Get a Sony or Panasonic or something midrange or above from one of the other proper big name TV brands. Do a bit of research. Avoid anything that is badge engineered from a Chinese or Turkish factory.
For more info on your rights outside the manufacturer's warranty then start here:
LINK