Thanks guys - it's very re-assuring to have the benefit of all your wisdom!

I am hoping it's just their way of working out the "pecking order". There hasn't really been any change in their routine, and they DO put their differences aside every time the fridge door opens, when they will stand right next to each other and beg for ham! Unfortunately it seems to escalate at night, and had been keeping us all awake. For the past couple of nights Connor has been sleeping in the utilities room (NOT as bad as it sounds - it's the size of a small bedroom, and his favourite nap spot anyway), and Ally has been in the kitchen, with their own litter boxes, food and water. Should I continue to separate them for a couple more nights and see if the situation improves?

One other weird thing - they both almost always use the same litter box - the new one I bought when we got Connor. Ally's box is usually clean when I go to scoop it. I never thought Ally would share a box with Connor, as he is a real stinky-butt!

Thanks again everyone for your advice - I feel much better just knowing that it's not only my two who act like this!