Martin, I think the figures are a little bigger if you count the French troops - which were not French, mostly Légion units - then the figures raise up until some 78.000 casualties until 8 o'clock in the night of July 1st 1916. And taking into account the men killed that day and the ones who died later, the figure raises until some 32.000 people killed.
That's true - but, without denigrating the French sacrifice, 1st July 1916 is remembered as the British Army's greatest disaster.
And indeed it is. And it was mostly a British effort. The French were very busy, being bleed to death at Verdun. July 1st 1916 is the blood bath of the Brits as Passandæle is the Kiwis' and Gallipoli the Aussies'. That's why WWI - I still - say was bloodier than any other war EVER...