It is understood that if your vehicle has been issued a Q reg within the last 12 months. It is possible to replace it if you can submit the relavent evidence. As layed out on the 'New Registraion Application' Page.

If your vehicle has held a Q reg for over 12 months. Then having it changed can be harder, but one owner has been successful in the past.

Google - "Exceptions: A Q-plate can only be removed if you submit new, conclusive documentary evidence to the DVLA that proves the vehicle’s original age and identity."

It is understood that it is at the DVLA's discretion on whether to remove a Q reg. Hence, I advise supplying as much paperwork as possible, listed below, to provide strong evidence. Only providing some of the paperwork may result in them bouncing the case back and closing it.

If your vehicle has held a Q reg. for over 12 months. Then I advise submitting the following paperwork to DVLA.

Cover letter - explain in brief that you are submitting new evidence to prove the age of the vehicle.

Do not state that the vehicle is a rebuild/kit car. It is acceptable for it to be restored/rebuilt from NOS original pattern parts etc.

Photos of the complete, road running vehicle & vin number.

Original brochure.

Apply for the vehicle History/B Card from the RLC archive - DIS Date In Service.

Apply for a replacment Disposal Form - DVLA recognised doc.

MOT done on the VIN/Frame Number - DVLA recognised doc.

Have a vehicle age verification inspection. The MVT (Military Vehicle Trust) & VMCC (Vintage Motorcycle Club) offer this service - DVLA recognised doc.

MVT - https://www.mvt.org.uk/contact---verification-officer.html 

VMCC - https://www.vmcc.net/library-and-dvla-forms 

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://vmcc.net/File/252/en-GB&ved=2ahUKEwj6_Ymak_WSAxUcTEEAHWl1BRAQFnoECBwQAQ&usg=AOvVaw3g5D-gYpICCgRfL4iHOu0z 

With all of the above evidence, it should provide a strong case to have your Q reg amended.

If the bike has been off the road for a number of years, perhaps on SORN for 10 - 15 years.

It may be worth to 'play ignorance', pretend the bike hasn't been registered before (barn find). And apply for a new registration as per details on the New Registration Application page. Along with supporting age doc.

The website 'is it nicked' has a vin & reg search engine.

It also details which month & year the vehicle was registered. To check if it has been registered in the correct year.

https://isitnicked.com/