Von, it might help you to know that UK Postcodes follow the format of ...
1 or 2 letters followed by 1 or 2 numbers then a space , then 1 or 2 numbers ending with 1 or 2 letters.
So it would seem it's the 6 at the end of yer postcode that's wrong. Using the link Bev kindly offered, I input G instead of the 6 but that comes back as no code known.
You can try all variations in 'find address' - NE3 5Pa, then NE3 5Pb etc till yer find the one yer want, or can use 'find postcode' instead and input the first line of the address and the town and it'll give you the correct postcode.
Hope this helps.