The first day of the battle of the Somme claimed something like 60'000 victims.......(Including my great grandfather).
I think there were more than a million casualties at the end.I dont think the British army has suffered caualties like that anywhere else.....so as far as the British are concerned that was our bloodiest battle.
Anyway heres a list of the bloodiest battles according to Wilkipedia.
List of battles by death toll - Wikipedia, the free encyclopedia