How to prep old cracking paint for repainting

[PaintyKate]

We've removed a decorative wall paper strip and it's taken a load of paint with it. There's also patches of blown paint in other patches. I've scraped off what I can (took these photos before I had scraped it all) but I'm worried as soon as I stick a roller over it, it's just going to pull more off. What's the best way to deal with this please? We have this problem in pretty much every room. I'm guessing there was no mist coat done?

 

[Wayners]

This can happen and most paints can come away a bit sometimes.
I'd fill over. Sand smooth. Acrilic primer undercoat the entire wall and see what it's like. If all good emulsion

 

[michealangelo]

Mist coat or thinned acrylic primer on patches before anything else or its going to happen again

If you feel it needs filling then you can go ahead knowing it won't crack or dry

Sand back to a required finish

Then thin emulsion or primer on filler areas

Then emulsion

It's almost always a lack of a mist coat