A V5 is not proof of ownership, is motor insurance in my name on the registered vehicle adequate?

No

When bailiffs clamp a car that does not belong to the debtor, they place a very high burden of proof on the owner to prove that they own the car.

A V5 document is not proof of own ownership, and it even states this on the front page.

Bailiffs often ask for insurance and car tax documents, but these carry little weight with the court if the bailiff disputes the owner's third party claim.

The best evidence that trumps everything, having possession of the car service history documents in the owner's name, which proves the owner has been maintaining and servicing the car.

The next best evidence is the bill of sale, or invoice, for the car, showing the date of purchase.

This should be accompanied by evidence of the flow of money from the buyer to the seller on or near the date of purchase.

If a bailiff still disputes a third party claim, the owner makes a third party claim, and the bailiff and the creditor are liable for your costs and damages.^[1]

^{[1] See Making a third-party claim to controlled goods}