Thanks to google I found this entry on a medal auction website (Dix Noonan Webb)
"H.M.S. PRINCESS MARGARET berthed at Riga on 19 December 1918, where she landed her marines on the 27th who, accompanied by an armed party from H.M.S. CERES, marched through the town. The following day frightened British subjects began to arrive on board. On the 29th it was heard that a Lettish Regiment had mutinied, and arrangements were made for the defence of the approaches to H.M. vessels by the aid of search lights, and the use of star and lyddite shells. Even more refugees joined PRINCESS MARGARET that night, bringing the total on board to 392 souls, 143 men, 169 women and 80 children. From 30 December to 3 January 1919 armed parties were constantly landed to police the town and so ward off menacing parties"........read more here
The internet is such a wonderful thing isn't it. I must have googled HMS Princess Margaret several times but then every now and again something brilliant appears....of course it's given me lots of new areas for my "research" ..........landing parties?.......HMS Ceres?