First off - Thankyou very much for the reply and the help.

Can i not just cover the smaller stones, after getting rid of as many as possible, with some new soil and sow the grass into that.

Im in Westminster, London. The rock is not natural.
It is in a garden and it all runs down a drain which is known to become blocked.
Erm, as i say im a new gardener but most of the grass to me feels quite light and dusty.

I will try your suggestion with the large riddle, I did have that one on my mind.

Thanks for the details on composting, that was something i was curious about.

Are the birds really that much of a threat? Again, im a new gardener so im not sure on this stuff - should I/can I cover most of the seeds with the soil or do they need to sit on top?
Best time of the day to sow?

"Yers. If you put as much energy into doing the job, you should have it
done tomorrow..." - the grass takes atleast 14 days!

Thanks for the help I will have some pictures of the progress online soon.