You’re correct about the EU ruling, but the CRA encompasses and surpasses it. You could chance your arm with it, but you shouldn’t have to.
Under the consumer rights law any item bought has to last a reasonable amount of time, no matter what the manufacturer warranty is
For example large electrical items like TV’s washing machines etc… are around 6 years
This isn’t quite right. Rather, you have up to six years to make a claim, it comes down to “reasonable” as you say. It’d be reasonable to expect a £1,000 washing machine to last 6 years, a £100 machine not so much. I’d argue that a dishwasher failing after 20 months isn’t “of reasonable quality.”
I’ve had a 100% success rate over the years with the phrase, “just so we’re clear, can you confirm that you are refusing to honour my statutory rights?”
we have an engineer’s report saying it was either assembled incorrectly or the materials used during assembly were faulty.
You’re on solid ground here. The CRA states that after 6 months it’s the consumer’s responsibility to prove that the fault was inherent at the time of purchase (if this is the angle you’re pursuing). You’ve done exactly that, they don’t have a leg to stand on.