Thanks for bumping this, Pasta.
I have to say, Kitty, that patching-up emulsion rarely works well.
Ok, if it's very new, then maybe paint from the same batch might be successful, but usually, it's all too obvious.
Assuming it's water-based emulsion, then a heavily diluted coat is all you need for a primer. (Maybe 4 or 5 of paint to 1 of water. Could be more water if it's a "trade" thick emulsion.)
First, I would look at why it's flaking.
Damp?
Newish plaster that's not been primed properly.?
Give "patching" a go by all means, but you may not want to live with it.