Do British people know what Stradivarius is?

Well, my original comment was that you don't have to be into classical music to know instruments. The violin has been used on many pop and rock songs - so while it might technically be a more traditionally classical instrument, it's certainly not tied down to one particular genre. And it's not uncommon for music fans to be interested in the instruments that musicians use, like guitars for example. And if you were talking about guitars, you might start to discuss popular or even legendary models of guitars, like the '59 Les Paul. Then the conversation might include talk about how rare and valuable they are. And if you wanted to do a comparison with another instrument that's very rare and very valuable, the Stradivarius is perfect. And that person says "The '59 Les Paul is as rare as a Stradivarius." And now you have two options. You either know what a Stradivarius is and you acknowledge or debate the comparison - or you stand there in silence because you don't know what a Stradivarius is. So there's your real world example of how knowing what a Stradivarius is can be useful to somebody who isn't a violinist. You could also use the comparison if you wanted to talk about a car or indeed anything of rarity and value. I hope that's answered your question. Knowing things is good because you can apply the knowledge to unrelated situations.