Just had a lovely local plasterer call round, named Thomas Braysford. He's fully professional, wants no cash up front and will provide full receipt. He acknowledges both rooms only need a skim coat and it will take him up to two days and can start end of this week. He's quoted £300 including materials.
I think this is a fair price and v. grateful to Accy Web for helping me find him!
Let's see if I'm still smiling next week...