In Spink's Coins of England (Decimal Issues), your specimen (with obverse by Ian Rank-Broadley and without denomination) is recorded as H29 and, as Pete stated above, it was issued in the various Royal Mint folders.
Coins with obverse by Jody Clark are recorded as H31, also without denomination although the Battle of Britain 50ps struck for circulation did contain the denomination (50 PENCE) .