Pesky weed in lawn.

Hi.
I grew a lawn from seed in May of this year. All was well until September/October when this weed started spreading quite rapidly. Does anybody know what it is and the best way to get rid of it?
Thanks in advance.

 

Looks like Bittercress Bittercress

 

Thank you. I'll now look into how to eradicate bittercress!!

 

Check it out, as I've not seen it as a lawn weed before, but in open ground and amongst pot plants. If it is Bittercress, be careful about seeds being sent flying into your eyes.

 

I think there is a strong possibility that you were right about it being bittercress. I think that I unwittingly spread it from the border when dug entire garden over earlier in the year. Thanks.

 

I think it will disappear once you start close mowing the lawn, I've got lots of it but never in the lawn/grass.