2009 Polo key coding

Hi fellow VW enthusiasts
Recently bought a 2009 Polo 1.9 TDI with only 1 key supplied.
Seller said he had the other one put away since new but couldn't recall the "safe" place he'd put it but that he would find it and he would post it to me when he did find it.
I now have it and find it remotely unlocks the doors, allows the motor to crank but not to run.
There is an orange "key" light illuminated and the orange "Glowing Wire" (glow plug) light illuminated.
Thinking it may have sat in a cupboard for up to 7 years, I replaced the key battery but no change .
Could the key have "decoded" itself due to lack of activity ?
Do I now have to make an obligatory visit to my nearest VW dealer for a key coding?
Any clues from my wiser peers would be greatly appreciated.
rory

More than likely VW can fix it for you

Definitely get it to VW to see what's up.

The keys can fail from time to time, so you'd be up for a new key. The remote part you can swap over onto the key, though.