Is this a stupid idea on how to get a great car on finance?

So I was listening to a radio station in London that says the rule of buying a mortgage is to buy a house that is 3 times the amount of you salary so I thought as I earn £24k a year would I be a stupid I dea to buy a car up to the value of say 50k as it wouldn't be 60 because I'm thinking of tax and insurance. I stay with my parents as the market for housing isn't good so is the idea stupid and if so what would you need to be earning to gain a 50k car?

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