Can anyone tell me the differece between Quartz tiles at £80 sqm and £40 sqm

£40/sq mt.................

I'd think if the question was based on the same make of Quartz from different suppliers then it would be down to their mark up and distribution/overheads.
I'd purchase a sample of both price range and compare and if off the internet confirm the sample is the stock item.
In general the price 'could' reflect the quality of the tile but that is not always the case.
Other members may have purchased this product from one of your tile suppliers, so if you'd like to provide more information to this thread a more sensible reply then mine may be forthcoming.

In the world of Ebay you often see a tile cutting machine for sale with a price of around £750 but then an identical machine for £1000....Go figure....They are exactly the same just that the higher priced seller is waiting for someone with too much money than sense to come along.

Now with your tiles the same thing may apply but without knowing if the £80m2 tiles are exactly the same as the £40m2 tiles then its hard to say. The market is flooded at the moment with this type of tile and the quality varies enormously . You really need to know what you are buying for your £.

Thanks for the quick reply i have sent for a sample from a company not far from you ie Durhan Crystal Stone £39.99 sq m and i have one from Stone superstone in Manchester same price. They are Black Quartz for a kitchen.I have also looked in Topps Tiles £6.90 a tile special offer, Al Jurad £9. a tile & Tile Depot £14. but would price match?? not knowing what to look for hence the question