I remember Mary Berry saying if the butter is "too soft" ( a classic mishap in the microwave) the biscuits will spread.
Mary's Butter Softening tip
"Simply cut it up into cubes straight from the fridge and place it in a bowl of tepid water (not hot- trust me, hot water makes a BIG mess!). Leave for just 10 minutes -usually the time it takes to measure out the rest of a cake ingredients, drain the water away and it’s perfectly soft and ready to use."