Can bailiffs take a car which is registered to someone but insured by the debtor?

No

Bailiffs may take control of goods only if they are goods of the debtor.^[1]

Being insured to drive a car does not confer any ownership, or beneficial interest,^[2] in it.

Even if the debtor has a right of use of the car, references to goods of the debtor do not include references to trust property in which either the debtor or a co-owner has an interest not vested in possession.^[3]

If a bailiff takes control of a car that does not belong to the debtor, the owner can make a third-party claim.^[4][5]

^{[1] Paragraph 10 of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[2] Paragraph 3 of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[3] Paragraph 3(2)(b) of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[4] Civil Procedure Rule 85.4
[5] See Making a third party claim to controlled goods}