I'm new to ponding and very new to pond filters.

I've got a cheap pond filter which incorporates a UV lamp, some foam and
some rocks. Water is pumped from the fountain through the filter and back
into the pond. I have 7 smallish fish in a 400 gallon pond.

My question is this - do I need to keep the filter running 24/7 during the
winter? I live in London. Mild winters, average overnight min -4deg C,
average day temp 5-10deg C

Nick