Hi --- In my view the credit card company employee you spoke to is wrong and perhaps unsure of the full implications of the consumer credit act 1974..... you have entered into a three party credit agreement by paying this deposit with your credit card, therefore you are not obliged to go ahead with this contract because the rest of the balance depends on you obtaining further finance, meaning you have a right to cancel and have the deposit returned, before the contract is concluded.
I suggest firstly that you speak to someone at the OFT below or your local trading standards for free, explaining the situation, before involving any expenses with Solicitors or the courts.
http://www.oft.gov.uk/oft_and_cd/
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Additionally : having re-read the DS regulations below and you not having delivery of the car yet, you may want to try getting your deposit returned by contacting the dealer and quoting the below extract, only thing is I can't find reference to a car under these regulations, however a car should be classed as Goods.
Under the Regulations a consumer can cancel a distance contract at any time during the "cancellation period" by notifying this intention to the supplier in writing. A contract which is cancelled must be treated as if it had never been entered into by the consumer. For example, if the consumer has entered into a credit agreement in order to purchase the goods, that agreement must also be cancelled at the same time as the distance contract.In both contracts for the sale of goods and contracts for the supply of services the cancellation period referred to above begins with the day on which the contract is concluded. However, the duration of the cancellation period varies depending on the stage at which the written confirmation and additional information is provided. The following is an outline of the various cancellation periods that may arise.
Therefore you could send written cancellation to the dealer.... you have seven days after delivery of the goods, but as you have not yet even received the goods you could try that.