It's a 'Silver Jubilee' Crown, (25 yrs as Queen) and was made in Cupro Nickel for circulation, Cupronickel Proof, and Silver Proof.
Have a look here for values of all 3 types. http://www.coins-of-the-uk.co.uk/values/deccr.html The values given are in UK£
Actually try this a see if you can notice a difference:
Get a clad quarter place it next to crown. then place a white tissue over the two coins. the clad should appear gray if the crown is silver it should appear white. not very scientific but it works on most silver. (cribbed from the "other" site, author is nohope, so I'm sure he won't mind me posting it here)
Let us know if you've scored a proof silver