https://www.thegazette.co.uk/notice/2505989
BY THE QUEEN A PROCLAMATION DETERMINING THE SPECIFICATIONS AND DESIGNS FOR FIFTY PENCE COINS COMMEMORATING THE ONE HUNDRED AND FIFTIETH ANNIVERSARY OF THE BIRTH OF BEATRIX POTTER ELIZABETH R.
(snip)
3. The designs of the said coins shall be as follows:
For the obverse impression either Our effigy with the inscription · ELIZABETH II · D · G · REG · F · D · 50 PENCE · 2016 and for the reverse designs either:
(a) a portrait of Jemima Puddle-Duck with the inscription JEMIMA PUDDLE-DUCK;
(b) a portrait of Mrs. Tiggy-Winkle with the inscription MRS. TIGGY-WINKLE; or
(c) a portrait of Squirrel Nutkin with the inscription SQUIRREL NUTKIN.
The coins shall have a plain edge.
4. This Proclamation shall come into force on the sixteenth day of March Two thousand and sixteen.
Given at Our Court at Buckingham Palace, this fifteenth day of March in the year of Our Lord Two thousand and sixteen and in the sixty-fifth year of Our Reign.
GOD SAVE THE QUEEN