Posted: 27/07/2015 at 18:58
Hi & welcome to the forum AJP
You have a few weeks before you put down your new lawn so may I suggest you use that time to dig over your garden - at least twice.
It is worth emphasising (as others have already said) that you will probably find all sorts of stuff under that topsoil. If you spend time digging now you can remove any lumps of concrete, wood, broken bricks etc etc. You can also see if you need to dig in any extra organic matter and work on getting the soil level and raked into a nice, fertile tilth - all this will help grass seed or turf romp away. You can also use the time to monitor whether there are any areas with potential drainage problems (ie does water puddle anywhere & take ages to drain away).
If you don't prepare the ground properly now you will forever have little uneven bits underfoot where stones and bricks work their way towards the surface. They may even start to snag and damage your lawn mower. The lawn will be patchy with discoloured or 'thin' areas where the grass gets uneven moisture & nutrients due to the stuff under the soil.
As Gary said you can use excavated stones and bricks as hard core under future paving etc. Once it's dug and raked you can come back to us and we'll remind you about raking and treading to compact the soil (so you don't get air pockets) and general last minute preparation before you go green.
So first purchases on my shopping list would be a decent garden fork and a general purpose garden rake. I would also start looking at lawn sprinklers in case we have a dry autumn and you need to buy one in a hurry - quicker to buy if you've already worked which one best meets your needs.