Well now you've probably jinxed it you wally!
Found some info on the net. And its looking like this is whats happening for difficulty settings.
Normal: Harvet 100%, Enemy Damage Dealt 100%, Enemy Damage Recieved 100%
Hard: Harvet 75%, Enemy Damage Dealt 150%, Enemy Damage Recieved 87.5%
Very Hard: Harvet 66%, Enemy Damage Dealt 200%, Enemy Damage Recieved 75%
There may or may not have other differences.
My Shopto order just arrived to my house.. for gods sake lol. Do Tesco take returns on unopened games If I have the receipt?