They can occasionally take time, but not this amount of time, something is wrong. Contact Sainsbury's insurance and insist on speaking to a manager, do not be fobbed of in any way. Advise that you have taken out insurance and that it's not showing on MID, as a result you could have your car impounded and be fined for no insurance due to Sainsbury's incompetence. Have them go through all your details, your vehicle registration (I would hazard a guess and say this has been taken down incorrectly) and make sure everything is as it should be. Raise a complaint and advise that you wish for them to note it as a "chief executive complaint". Also, call the Financial Ombudsman Service and raise a complaint, they will advise they cannot look into it for weeks but that does not matter at this time. The FOS will then contact the insurer, they will get charged £500 by the FOS for having an open complaint. At this point, things should start moving as they now realise that if they do not resolve, it will cost them £500. Advise your insurer that they will need to provide a hire car for you and insure it in the mean time as they are denying you the use of your vehicle.