Andy -

015. The flowers do look like greater stitchwort, Stellaria
holostea, and the date fits. However, I can't make out suitable
leaves in your photo -- and if the leaves visible creeping along the
ground are the same plant, it's not stitchwort. What about field
mouse-ear, Cerastium arvense? Are the styles visible in the
original? Does it have three or five?

021. Difficult to be sure without leaves. Does look like
cuckooflower Cardamine pratensis.

010. Yes, herb robert Geranium robertianum.

001. Yes, bird's-foot trefoil Lotus corniculatus. The sepals are
visible and are clearly not reflexed (see my comment on Colin Duke's
recent query on UK Wildlife).

019. Lovely picture. Phew, 1.5 MB!

039. Yes, early purple orchid Orchis mascula. Obvious in flower --
can usually be identified in leaf by the spots being either round or
elongated lengthwise -- the Dactylorhiza spotted orchids' spots are
stretched across the leaf (if not round), sometimes even making
tiger stripes.

019e. Not harebell -- could be spreading bellflower, Campanula
patula, either wild or escaped. Habitat?

023e. Puzzling at first, as it appears to be much bigger than it
is. A small head of carrot Daucus carota.
028e. Selfheal, Prunella vulgaris.

030e. Can't really tell from the photo -- there are several similar
ones. Habitat? My guess is imperforate St John's-wort, Hypericum
maculatum -- there do seem to be lots of black glands on the petals.

044. Meadow cranesbill Geranium pratensis. Was this growing wild?
I didn't know it occurred in Sussex -- hardly any wild sites in the
SE, though common in suitable grassland in the west and midlands.
Very similar to several garden cranesbills, which are however
usually bluer.

079. Does look like charlock Sinapsis arvensis

Richard