Posted: 03/10/2017 at 17:52
On a slight tangent Andy - I wouldn't bother too much with anything right now if you're having building work done. By the time they've finished trampling it into oblivion, you'll need to dig the whole plot over anyway!
Sorry - that wasn't very helpful, but I doubt if the clay is having that much of an effect if you have that amount of topsoil on it. Excess water would gradually percolate away. If you're in an area of very high rainfall and you're using the grass excessively, I can see it would be an issue, but I think I'm siding with Dave a bit on this.
Is there a reason for getting a company in rather than continuing to do it yourself? I can understand if you're busy, but perhaps keeping it simple, and just doing some scarifying on a basic level, a weed and feed in spring, and cutting regularly would be easier, and possibly better.
I garden on clay, and we get a huge amount of rain, and certainly the front grass was very compacted and weedy when I moved here, but I don't do anything too major. I don't have too much moss, despite it's northerly facing aspect, and I only do a bit of forking and scarifying when I can be bothered, and it gets a weed and feed in spring, and regular cutting. It's easy to get a bit worried about grass too