Why are insurance quotes on comparison sites so high?

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I'm almost 17 and I'm hoping to learn to drive and get a car. I was looking online to see what the insurance might be on some possible cars (ford KA, fiat sciento, nothing too fancy) but the insurance quotes were ridiculously high. The cheapest was around £6000 for third party which is really high because so many of my friends have cars and their insurance ranges from £1800-£3000. Why is it so high and will it actually be this amount when I come to buy the insurance?

Why are insurance quotes on comparison sites so high?