Annual Meadow Grass
Meadow grass is a problem that even our professional growers come up against and have to try and manage with good maintenance as there are no longer chemical solutions to treat this.
Our advice to manage it as best as possible would be to keep the lawn cut regularly to ensure it is as thick and dense as it can be. Meadow grass will go from seed to plant in about 3 days and will get into any gaps or spaces. At this time of year it will be at its worst as it is flowering. If you try and keep your lawn short - mowed probably a couple of times a week, then this should help. You also need to keep it well fed with a standard NPK lawn feed.
Obviously once it is already in the lawn the only way to remove it would be to cut the biggest plants out but this will leave gaps so pop some seed into those gaps to stop the meadow grass from getting back in. Over seeding can help to prevent meadow grass as it fills in any gaps or spaces.