Weed killer before sowing grass seed

Hi everyone,
I wondered if you would mind offering your advice on weed killers for lawn establishment purposes? We're getting our garden dug over in a couple of weeks and the gardener we are bringing in had plans to weed kill the soil, and said we could plant our grass seed for the lawn a week later. However, online I've read that this can kill off earthworms and other insects etc. so I opted against using it.
I've just been reading up on wildflower establishment and a professional gardener was advising to use weed killer in the soil again before sowing the seed. I've found conflicting advice online as to whether it's a good idea to use weed killer or not, and how bad it is for wildlife etc so thought I'd check in here.
Thanks for any help and advice,
Lucid
Posts
Thanks for the reply hogweed. He was talking about applying weed killer and digging in one go - I'm not sure which order he would do it in. Is this not correct then?
Lucid
No it's not Lucid. Weedkiller takes a week to 10 days to start working properly. Weedkiller then immediately digging just buries the weed which can then come back, especially if they are perennial weeds. You can dig in annual weeds without applying weedkiller turning the soil as you go. That's the way I do it and I'm a professional gardener.
Thanks Dave. I think I'll leave it as it is then, and not get the weed killer done as the garden is already booked to be dug over now. I kind of assumed he'd meant he'd apply it to the surface once the digging over is finished, but it sounds as though that wouldn't be beneficial anyway. There is existing turf that will be removed so I'll have to hope that most of the perennial weeds come out with it.
Lucid
They will, as long as he digs out the roots of dandelions, docks etc. and doesn't leave bits of them in the soil.
Thanks Steve. Am hoping we can get the lawn off to a good start. I'm sure the odd weed will slip through.
Lucid