The full number is WDB9026622R781135
OK.... the radio code list that's posted in many places is for the *North American* Sprinters.
If it hadn't been posted (by a dealer), we here in the US/Canada would have to ask our dealers for the codes.
So, being in the UK, i suspect that that's your pathway: ask an MB dealer.
Note how your VIN pattern differs (a bit) from the North American decode page i posted.
You're still WD for company and county of origin, and i wonder if the "R" before the "assembly number" means right-hand drive?
(Australian members could confirm/deny that simplistic extrapolation).
Perhaps the UK 3rd party Sprinter Maintenance Manual provides a VIN decode ?
The VIN plate is attached to the drivers seat bottom left for RHD opposite side for LHD.
Here in the US, the VIN is put in many places.. and one is on the lower edge of the windshield/screen on the driver's side. It's riveted to the top of the dash panel. That's the one i use as "gospel" (partly because it doesn't require opening the door and hunting).
I also agree with Amboman... it's also placarded on the seat pedestal
This too-close-up view of mine shows it pasted sideways near the rear of the pedestal.
The black bracket on the lower left of the photo is the MB fire extinguisher bracket,
my vinyl-covered cargo floor is the grey on the lower right.
This shot was taken looking in through the driver's side door (left hand drive).
For what it's worth, the stickers on my engine do NOT have the VIN,
but i think there's one with it on the sheet metal near the hood (bonnet) latch.
--dick