Thankyou for all the replies.
Mist coat definately less well stuck at shoulder height where plaster more polished compared to corners of wall etc. Think this and only a 20% dilute mist coat contributed.
Sellotape really just an idea to see if you could tell how strongly stuck the mist...
Having applied a mist coat of 5:1 matt emulsion:water to newly plastered walls (done 8 months ago) I decided to test whether it had stuck prior to a light sand. Using sellotape there were some areas where the entire mist coat came off and others where it was firmly stuck. Is this a true failure...