First - I'm not a lawyer
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But again - be careful. For most dealers, I believe the contract is an agreement to buy a car at a future date - it's not a sale in itself. It's therefore entirely within their right to specify how the price might change before delivery - and they acknowledge that if it does change then you have the right to terminate the contract. All of that is entirely legal and compliant with the CRA. Also (and again, from the Ts&Cs from my dealer), they explicitly exclude liability for costs incurred if the contract is terminated (they do have to give you notice of any change). We may not like the Ts &Cs - but if we've accepted them unchanged by signing the contract then we are bound by them. The message is to agree a variation to them before signing (eg that the price is fixed).
Where you have leverage is that the dealer doesn't want you to terminate the contract and leave them with an unsold car, and hence may well absorb some or all of any price increase. But they are not legally obliged to do so.