https://trace.london/ i've never had to use this site fortunately. It's main use is to find if your car has been towed away by the council. I entered my own reg number as an experiment and got this:
"Vehicle registration not found
Vehicle registration *******has not been located on TRACE. Please check that ******is the correct vehicle registration number and try again.
If ******* is the correct registration number, and this is the first contact that you have made with TRACE to try and locate your vehicle, please try again in 30 minutes to see if there has been a delay in receiving the details.
If you have previously contacted TRACE on this matter and there is still no record of your vehicle please contact the call centre on 0845 206 8602 to speak to an agent."
This may be a valid use of a premium rate number as they are offering a potentially useful service but even if it's a legit use of 0845 they must declare the call cost.