Hang on. Someone kindly emailed me this:
If it was owned by an owner-driver it would only have to be registered with the DVLA as a private car with a private individuals name and address.
Assuming you don't want to ring all the borough councils in the north west :OP you could look for a few tell-tale signs.
Firstly, the car is petrol not diesel. Although if regulations allow cheaper cars to be used the fuel saving becomes irrelevant (our council demand that the car is less than 5 years old).
Look inside for taxi business cards. They are **** and get EVERYWHERE. Have a peek down the side of gearstick/handbrake gaiters… Every single one of my cars and every loan taxi I've had has had old taxi cards stuck somewhere.
It will have carried a local authority plate, so look for drill/screw marks around the back, or tape marks if it has been stuck to the window. Some clever holders sit beneath the number plate and poke out, so look for marks and scratching above and below the rear plate.
It may have carried door signs. These are magnetic and if you trap dirt, they mark the paint. Also check the bootlid (ariel fitment) for similar marks.
Anywhere marked in the dash/footwell area? They will have needed a radio, a meter, a cash tray (normally in the door pocket) a licence plate and poss a sat nav cradle. By the same token, look for disturbed interior trim where an ariel cable may have been run.
It looks like it has leather… If it's been a cab the rest of the interior will wear at a similar rate to the drivers seat. Baggy seat squabs? If it's cloth, be brave and put your face to the seat. Take a deep sniff and see if it smells of any of the following – kebab, baby milk, 9 year old farts, spilt beer or puke.
That's all I can offer short of actually checking licence records. Might be worth firing off an email to each of the licencing officers to check
I did this last bit- go onto a few local councils websites -type in 'Taxi licensing' then ping them a nice email with the reg number asking if that reg has EVER been listed. You will get confirmation back either way.
Do it for a few boroughs though.