They told me and the misses that its down to the economy and the amount insurance companies had to pay out during the winter months. I think thats a rubbish reason to charge me double.
I think insurance companies look to actually make money on a particular customer from year 2 onwards. For new customers, they need to 'hook' you in with a super low premium offer knowing that they may well be loosing money in the short term.
The number of offers 'guaranteeing' to beat your renewal quote and draw you in with introductory offers is testament to this and why everyone always says, never simply let a renewal run its course - always shop around. Despite this, the insurance companies know a certain percentage of their new customers will simply renew and bingo - they make a mint.
Look out for RAC policies now - they don't just write to you with a renewal notice, they actually take the money automatically from your credit card; the policy small print says you need to write in advance and cancel the renewal before its due.
On the whole, I've always seen my renewals go up, but never double - seems a bit daft as smaller increases over several years will eventually see a £500 premium easily reach £1000 if left unchecked. Hitting you with it in one swift swoop is a bit harsh (though it might well be an 'experiment' to see how many of their customers leave instantly - these things do go on).
With a bit of effort, I'd say anyone could get a good quote on their insurance (relatively speaking of course; a 17yr old with a GTA is always gonna be expensive). Don't just rely on the price aggregators (e.g. MoneySupermarket), do the calling yourself and charm a good price out of the person your speaking to. UK call centre are best for this tactic.
I even heard that phoning an insurance call centre in the morning will get you a better price. Late the afternoon just sees everyone tired (big lunches?) and nearing the end of their shift and they'll be buggered if they wanna spend 20 minutes bartering with customers.