I was gonna say - we did that almost two years ago but not much happened - I'm guessing it takes a good while for them to fight their corner against anything that's already there? I keep seeing stuff about yellow rattle helping them get established... anyone done that?
Funny you should mention that. I've got loads of it starting to flower at the moment.
I sowed them along with the other flowers. They parasitise various species of grass, helping to open up the sward, therefore giving other plants a chance to grow.
I'm actually thinking of cutting mine out, as I have about 7 different species of grass in my lawn, most of which are nice ones (fluffy and soft when in flower). I am lucky that my garden is on somewhat poor, acidic soil (good for nice grasses, wildflowers and wildlife).
The bog standard lawn mixes usually consist of the rye grasses. Tall, vigorous and rich green in colour. Yellow rattle will struggle against them, but it's worth a go. You must get the mowing regime right too.
The bees are all over my yellow rattle, so I'll leave it in for a few years and see how it goes.