Me and DH are replacing the gravelled area in our back garden with a small patch of lawn. DH has removed the bulk of the gravel and put it into sacks. But there is still a fair amount of gravel left half buried in the ground - see pic hopefully attached.
Am I right in thinking that we need to get rid of all this gravel? I heard you can get drainage issues in new builds because builders leave random stuff in the soil (bits of bricks etc) and wondered if this might have the same effect?
I should add we do live in a new-ish build (2003) so I'm not sure what the quality of the soil is like and keen not to make it any worse.
DH says it doesn't matter because the gardener will add soil on top 
We are getting DH's friend to do it who advertises himself as a gardener, but has only been doing it a couple of years and he's not an expert so I'm not entirely confident...