Frozen water butt

Looking around outside 'our' flats just now; during the summer we put in some water butts to do our bit towards conservation mainly for watering our Tubs and flower baskets.
Of course when they over flowed this is what happened... frozen I know the water is also frozen inside and am wondering whether they may split with the pressure.
Remains to be seen at least its outside not like some people who have burst pipes inside.