DVLA issues 'Q' registration numbers to vehicles whose age or identity is in doubt. If this happens, any original vehicle registration number will become invalid and you must not display it again. To get a 'Q' registration number, your vehicle has to pass a type approval process.
We're the Driver and Vehicle Licensing Agency (DVLA), holding more than 49 million driver records and more than 40 million vehicle records.
About us - Driver and Vehicle Licensing Agency - GOV.UK https://www.gov.uk