Looks like the same exact charger going by the specs, but only looks a tad different with the ridge on the European one and the plug part. But electrically they are exactly the same.
Why the difference in price? That is the question!
Edit: Checked the amazon.uk store and they did offer this charger at 8.99 pounds if bought at the time of buying the fire.
You may try to call amazon and see if they will sell you these adapters at the lower cost?
Who knows they may do it!