You could try the National Equestrian Database (NED) as this is the only central database which stores information on all horss in Great Britain (Well those that are passported).
No idea but pet ID have database with owners name/address for microchips so might be worth giving them a ring. If it's not your horse they might not give out any info cos of data protection though.
You most certainly can - after many efforts trying to get the KWPN to give me information as I had been told that our mare was KWPN registered - I gave up and started searching all the microchip people I could find on the internet - I eventually came up with all my horse's details - via EUROPETNET - if your horse is not british born you may find that you will be able to trace it - what does the microchip number begin with??
If your horse is European you can try "Stiching CHP" they are Dutch but very helpful if the number matches one of the European studbooks as they will provide you with the contact details of the relevant society
You could try the National Equestrian Database (NED) as this is the only central database which stores information on all horss in Great Britain (Well those that are passported).