"mattyh" wrote in message

So I'm best off getting rid and buying some proper topsoil?

No. Use it. I don't have more than about an inch of stuff that could
be described as "topsoil" and even then it is only a darker colour
than underlying poor, decomposed ancient rock or clay.

When I make a new bed, I just turn everything and leave it in place
and then start adding manure and sand. sometimes I'll top it all with
leaves and anything else that has ever lived and leave it and
sometimes I jsut add all these things and start turning and turning.
Any weeds or old grass that pops up alive is weeded out and its all
turned again etc. Virtually a situation of sheet composting or big
sloppy compostng on top of the ground.

Can't I kill it off with some weedkiller?

You could but you also do it by some hard work of turning that breaks
it up too.