Identify a weed please

Hi, I really know nothing about gardening, but have decided to have a first go at planting various seeds and bulbs. As a first attempt, I chose them purely on height and colour, so I'm not even sure what I've planted (I threw away the packaging after I planted them).
Anyway, various things have started sprouting all over the soil since the warm weather arrived, though I'm sure a lot of it is weeds. Can anyone confirm that these five photos are of a weed, and identify it if possible? If so, I'll pull them all up tomorrow, unless I shouldn't?
It would be nice if someone's website had a gallery of common UK garden weeds in their early stages of sprouting so that newbies like me can identify them more easily, especially when we don't know any names or even if an early shoot is a weed or a flower. Unless it has course nettle-like leaves, I'm never sure what it is until it's fully grown.
I've noticed a few other very small sproutings which I'm sure are flowers from seeds, and a couple of sprouting bulbs, so hopefully some of what I planted will end up flowering in a few months... depending on how many the cats and foxes destroy.

Edit: For some reason, the link I try adding doesn't appear in the message. Here's one of the photos of the (probable) weed.
Posts
That is too young to tell. It hasn't even got it's true leaves yet. Most seedlings start like that, could be one of your seeds!
Some seed leaves are quite distinctive but we'd need to see them from the top which is how you see them when you're weeding
In the sticks near Peterborough
I've come across this website, written by an amateur gardener for other gardeners. It has a bit about weeds with photos and other handy bits such as seed sowing.
http://www.gardenwithoutdoors.org.uk/?q=weed_guide
Indeed yes, some of the old favourites there, including my main offender, enchanter's nightshade
In the sticks near Peterborough
Thanks for the replies! As I can't link to a page with the other four images, I'll have to insert them here:
I know I was taking a risk when I plucked it, but I took it from a cluster of such sproutings, so if I've lost a flower then hopefully it won't show too much.
Thanks for that link, Busy-Lizzie! I'll try to compare what's growing out the back with what's on that page.
I wonder if my photos are of 'fat hen', as shown about half way down that link? There are more leaves per sprout on those photos, but my ones have only just appeared above the soil.
Non the wiser after the latest photos, seedlings too young, no true leaves yet.
my guess, as that is all you can do is guess with a seedling that size is that it's some kind of tree seedling. Due to the stirdyness of the stem/root/leaves. But yes you need to wait for the second set of leaves before you really have a clue.