Mowing regularly usually gets rid of most weeds. They say you can transform anything into a reasonable lawn, just by mowing.

I would pull theses out as it may be below the level of the mower blade? if so lift it with a rake before mowing, you can also try a lawn spot weeder.

Could it be an oxalis? Does it have clover-like leaves? Very difficult to get rid of, if so.

Oh Beattie, I just wish that were true!

You mean you want to have Oxalis corniculata in your lawn Steragram?
http://www.dgsgardening.btinternet.co.uk/sorrel_creeping_wood.htm
If you did I think you'd change your mind.....

I used to have a decorative species of Oxalis but it proved to be tender and I lost it, but most Oxalis species are tougher and this particular, yellow flowered creeping one is a right pest!

Possibly a creeping buttercup? I bought one of those lawn weeder things (try googling grampas weeder) it's doing a great job, gets all the root out.

It could also be Medicago lupulina or 'Black Medic'. Same clover-like leaves. Tiny yellow flowers. A real pain to get rid of. It's an annual weed but produces so many seeds that it just keeps coming back. Grows too low for the lawn mower to trim it back. Selective weed killers are on the market for this.

No Beattie, I have it popping up in plant pots here and there but have almost got rid of it. I meant i wish it were true that mowing gets rid of most weeds. I'm happy for you if it does in your garden but it doesn't in mine.

This was just a theory I heard on Gardener's Question Time many years ago. I've never aspired to a "lawn", just a bit of grass is all I've managed.

Good old GQT. My front lawn is mown regularly and it has celandines, dandelions, bugle, ragwort and even a few primroses. It looks very nice for a couple of days after mowing and after that I just get a guilty conscience because i still haven't weed and feeded it.