Usually the plate itself is not a major rating factor, but you should tell the insurer when the registration number changes. The important point is to make the policy describe the real arrangement rather than the simplest answer on the form.
Why this can be an insurance issue
The insurer identifies the insured vehicle partly by its registration. When a cherished registration is assigned or removed, the policy record needs to match the vehicle's current registration details.
Motor insurers price a bundle of facts together. A detail that looks minor on its own can matter because it changes who controls the vehicle, where it is kept, how often it is driven or what the insurer may have to pay after a claim. That is why two insurers can react differently to the same situation.
What to put on the quotation
Contact the insurer promptly after the DVLA change and ask for updated policy documents. Some insurers may charge an administration fee.
If the online form does not give you an answer that truthfully fits the situation, do not force the nearest convenient option. Complete as much as you can and check the point with the provider before buying. Keeping a note or email confirming an unusual arrangement can be useful later.
What can go wrong
Do not assume the database will update automatically. A mismatch between the policy and registration can cause unnecessary trouble after an incident.
The problem with an inaccurate answer is not merely that the premium might have been different. If the undisclosed fact is relevant to a later claim, the insurer may investigate whether the policy was written on the correct basis in the first place.
Will every insurer treat it the same way?
No. Underwriting rules differ. One provider may accept the arrangement with no difficulty, another may charge more, and another may decline to quote. That variation is one reason a comparison can be useful when your circumstances are a little outside the ordinary.
Before you buy
Read the main policy information and check the excess, level of cover and any condition connected with the unusual part of your situation. A cheap quotation is only useful if the policy actually reflects the way the car is owned, kept and used.
See how different insurers respond
Enter the details as they really are and compare the quotations and policy terms offered for your circumstances.