I am posting this under United Kingdom Coins as they were minted in the UK.

The Birmingham Mint was involved, along with other European mints and blank manufacturers, in defining the technical specifications for the blanks used for the new Euro coins. The original specifications were adopted in May, 1998. After consultation with some stakeholders, the final technical specifications were adopted in February 1999. The Birmingham Mint Specimen Euro coins were minted on blanks from the original specifications of 1998.
The Birmingham Mint was vying to get contracts to supply blanks to the mints of Europe. They wanted to show potential customers the quality of their blanks. Specimen pieces were minted on actual Euro blanks the Birmingham Mint produced. There were 65 presentation sets made and distributed to mint masters throughout Europe. There were also around 10 'pouch' sets that Birmingham Mint employees carried with them as salesman's samples.
The European Commissioner who oversaw the quality of the Euro, saw these specimen pieces and deemed them to be counterfeit because they were the exact size, weight and metal composition of proposed new Euro coins. He ordered them to be destroyed.
Most of the sets were re-obtained by the Birmingham Mint and destroyed. There were a few sets unaccounted for and remain in private hands. It is estimated that less than 10 full presentation sets and a few 'pouch' sets still remain. Individual ones can be found that have been removed from the set.
The Birmingham Mint never officially minted Euro coins. They did however strike some 2 Euro coins for the Royal Dutch Mint in secret. The Birmingham Mint was already producing the blanks for the RDM but the RDM was struggling in striking the 2 Euro coin.
I received this information from Mr.Kevin Binnion who was the Engineering Manager of The Birmingham Mint, and oversaw the production of the Euro blanks and the collection and destruction of the 'counterfeit' specimens.