What is this and how do we get rid of it?

That is couch grass. Congratulations. Best to dig it out. Fertilizing and scarifying doesn’t help much against it. This type of grass usually grows faster than the lawn around it. If you are a bit consistent, you can temporarily get rid of the couch grass. But it will probably come back again as wind-dispersed seed. Best regards

Dig it out... we have so much of it, if I dug out all of it I would have a crater landscape :) probably only helps to patch up with topsoil and reseed the spots?

I see it more like Curly and don’t believe it is [Quecke]. You could initially try using fertilizer and overseeding so that the finer varieties come back up. I am not a fan of weed killer, and it wouldn’t help against [Quecke] anyway if it spares the grass. You could flatten everything with glyphosate and then dig it up, but then it won’t be really green again until September.

I see it more like Curly and don’t believe it is couch grass. You could first try fertilizer and overseeding so that the finer varieties come back up. I’m not a fan of weed killer, and it probably wouldn’t help against couch grass anyway if it spares the grass. You could flatten everything with glyphosate and then dig it up, but then it won’t be really green again until September.

I carefully dug some up at three different spots, attached are the pictures. I would have expected the long white roots typical of couch grass, but I can’t find any; are these then not couch grass after all?

This is not couch grass. Couch grass consists of individual stalks that spread wonderfully through rhizomes. You can only get rid of it if you dig out every tiny piece of the root or otherwise deprive it of a base, e.g., with a dense lawn layer. A lawn is made up of a collection of grasses. I also believe that it is a type of grass that is now spreading more than others due to the minimal care.

I would agree with that. We had that too. Simply mowing, scarifying, fertilizing, mowing, etc. will then disappear on its own.

Phew, I would say I got lucky again, started scarifying yesterday, fertilizing will still be done by the end of the week... then we'll wait and see. I hope the lawn mower robot, which is already waiting in the shed, will help the lawn recover quickly. Regards