Difficult one this, as I can't get a picture of the weed. They're starting
to come through now, light green broad leaves thrusting up through the earth
( the leaves come up directly, there is no central stalk, the leaves are
folded in half along the centreline as they come up ).
The stalks are not round IIRC, but more like lettuce stalks. In
fact, the whole plant resembles a lettuce ( not that you'd want to eat it )
eventually, with tongue-like leaves growing outwards and upwards. I let some
grow last year and they got to over a foot across., but I never saw any
flowers or central stalk. The young leaves are vaguely D shaped, slightly
finely serrated, maybe with a touch of red in the stalk occasionally. The
plant spreads by rhizomes, white, some 2-3mm across.
It's not Hairy Bittercress, Creeping Buttercup or Plantain. I don't
think it's sorrel or dock; I've got some Dock ( Wood Dock? ) growing and
that has more oblong leaves on round, reddish proper stalks. Sorrel has rear
facing barbs on its leaves which my weed doesn't, though mature specimens
have a somewhat serrated/spiky leaf outline.
Any ideas? I'm in the SW and on clay soil, and this weed is
ubiquitous.

Andy