Silver Proof Piedfort D-Day Commemorative 50p Coin

Hello,
I received a few coins from a relative some years back, and they've been hiding in my wardrobe ever since. I recently dusted them off and decided to sell them. I'm not particularly informed about modern coins, and so am compleyely paranoid that I'll sell a coin for slightly higher than bullion only to find out later that it's the coin equivalent of the penny black!!

I'd appreciate it therefore if anyone could fill me in on the value and rarity of the coin below:







According to the Certificate of Authenticity, there were 10.000 issued.

Thanks!