If your lawn has been weed free for more than 40 years without any kind of treatment then I have no explanation of how they appeared on your lawn that suddenly other than $&@/ happens. Aside from that fact of life, you can remove them by hand which involves repeated attempts but more realistically you will find chemical control the most effective. Since you live in the U.K. and I in the USA I will not suggest anything to you but leave that up to GOY flagship members to do. But, to be sure that it is self heal please post a photo of it to get an exact identification before considering any application to your lawn. You do not want to apply the wrong thing and you do not want to lay in anything that will be harmful to your lawn.

they have probably been there in leaf only for some time but the mowing has kept them hidden. a feed and weed type dressing has worked for us but it will need more than one application. cut the grass to remove the flowers before they set seed and make the problem worse.

welcome to GoY too

Thank You. Am still amazed at the speed this has spread! Just waiting for the chap who now cuts it for me. He has not yet seen it so should make his day!

If he cuts your lawn with his own mower and does others lawns too, the lawnmower could have been a key player in inoculating your lawn with this weed.

It invades one of our front lawns and does spread very quickly. We have used Feed and Weed and Weedol indifferent years.both work quite well but we usually miss a bit and it comes back. This year we have loads of violets too - very pretty but not the original intention! Soon be time for the Weedol again... We do our own mowing so its not from imported seeds.

PS If you have gone 40years without a weed in your lawn this must be something of a world record. How on earth did you manage it? Do you live in a built up area or more in the country?