I have a 8 year old cat (had him 6-7 years ago) and about 2 months ago i took in a 10 year old collie cross. The dog is very placid and shows no aggression towards the cat at all.

I started with the dog in the bathroom with a stair-gate across the door and this has worked well. The cat will now go into the bathroom and seems fairly confident with the dog - rubs his head against her, walks right underneath her etc.

However, if the dog is out of the bathroom the cat changes and becomes quite aggressive - he will chase the dog, jumping at her hind quarters and generally try to corner and intimidate her.

I don't want the dog to spend too much more time confined to the bathroom but how do i progress from here?

(I live in a flat, so everything is on one level)