Don't forget to arrange for transit insurance if you go down this route. Also, note that you can only keep your car in Greece for 6 months before it needs to be registered in Greece (and for that I think you need a residents permit and tax number etc). Also, you will have to pay local registration tax.
Also, if you intend to return the car to the UK after the 6 month period, ensure that either your UK road tax doesn't expire or you make sure that you complete the SORN. If you don't you will be liable to a fine upon return to the UK.