@Jim52 I personally don't see a problem with what you have done, in some respects you have helped your dad buy the car, so you have technically 'gifted' him some money towards the purchase, plus you are paying for the insurance. Probably the only issue is that the car is owned by you and not your dad, but you can admit that this was a genuine mistake and maybe something the garage did rather than you requested. To back yourself up, just keep a record of the purchase trail for any future questions if they arise.
However, in terms of assets, you can still say that the car is an asset of your dads and was purchased for his benefit. The vehicle can be sold at any point in the future and whatever funds you get from the sale could be paid into your dad's account, as long as you show no benefit from the sale there should not be a problem.
If I was you, just to prove the vehicle is being used for the benefit of your dad, I would keep a record of all the mileage/journeys etc you take and all receipts for fuel/maintenance etc.
I wouldn't worry.