The good news is you don't need to "hack the wall back" but you need to create some serious scoring/roughing of the surface. Use an old trowel or scraper & criss- cross score all over the wall, penetrating the paint & back into the plaster. Space the score marks around 20mm apart & when you’ve done that, go over the whole wall with a VERY stiff wire brush so it looks a complete & dull mess. Give it a coat of 3:1 PVA & leave to dry thoroughly for at least 12 hours, the longer the better. Just before skimming, PVA with a 5:1 mix, preferably applied with a roller but don’t over brush & skim when tacky.
You must, however, talk to your plasterer regarding prep. Work & what, if any, he’s prepared to let you do; then follow HIS instructions explicitly.