You can only report a vehicle with no MOT to the police if it is being used on a road.
You need the vehicle:
number plate (registration number)
make and model
The Driver and Vehicle Licensing Agency (DVLA) and the Driver and Vehicle Standards Agency (DVSA) cannot take action against a vehicle with no MOT.
What happens next
The police will investigate your report and the driver may get a fine. The maximum fine is £1,000.
For further information on Reporting a vehicle with no MOT can be found on GOV.UK's website.