I metre high patio by 10m-6m

The soil idea is a possibility, however, once the soil is moved it takes days/weeks to fully settle you could try to speed it up by using a large scale whacker plate but it will still take a long time before getting a proper solid base. Additionally, the best course may be hardcore covered by sub-base using a large scale whacker to fully compress it then build your patio off of that?

I'd sell the soil if it is any good as top soil. Worth about £40-70 per bulk bag and then replace it with any scrapings the local builders merchants around might have and look for cheap/free clean hardcore. Using soil that is not fully compacted will end in misery as the patio is unlikely to be water tight and will therefore let water through which will erode the soil. This in turn will create holes and channels in the soil and your patio will sink. Assuming you paid a small fortune for the slabs and mortar you will be forever spending money to rebuild it because the soil is not there... A nasty spiral will develop with a nice patio being ruined and repaired to look nice to being ruined as more soil goes and repaired again, ad infinitum...