Morning all. I am back from WorkingAwayLocation but due to missing the preferred train home by 3 minutes, I am running staggering about on 4 hours sleep. I may become slightly incoherent.
On the plus side, having been working, I had my laptop with me so got a screening report written up for you on the way home.
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Got into theatre and sat down. Much faffing. Saw someone looking v. much like Holliday Grainger sit down not far from us... 
"See that woman over there, she looks just like Holliday Grainger..."
Episode introduced, screening date announced (Bank holiday Sunday at 9pm) Episode starts - very v. good. Good music, much FAF, funny in places, etc. All very enjoyable. There are some differences to the book - at least one minor character missing, and a scene missing so it will be interesting to see how they work round those. Credits roll, people move about, lights go up... See-that-woman-over-there-she-looks-just-like-Holliday-Grainger has vanished, to come out through a door being introduced as Holliday Grainger (followed by Tom Burke). I'm sure she would be reassured to know that she looks like herself 
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Present on Stage - Holliday, Tom, Director, Screen Writer, Exec producer (not JKR, another woman) and the Chair.
First Q. noted that Holliday had watched the episode with the audience on the big screen - had she enjoyed it? (Yes because she hadn't seen the final cut with music before). Q to Tom - why didn't he watch it, didn't he like watching himself? Answer (somewhat flummoxed, erm, no, um, he'd preferred spending the time eating (I think he may have used the term 'in an eating frenzy' or something like that. which caused some amusement.) He certainly gave the impression that he doesn't like watching himself on screen, which we know isn't entirely true (S3 Screening)
Anyways, other questions -
Was JR involved - yes, on scripting level and some very specific comments, but otherwise she just let them get on with it, because she's a Very Busy Person.
Exec producer etc felt the pressure of not wanting to make a mess of it, being a JKR adaptation as did the other production staff. But they get the impression that JKR loves it, and was very involved with watching episode rough cuts etc. (She also provided unspecified advice about what characters were needed for future series to make sense - probably along the lines of her telling the Harry Potter screenplay writers that yes, they did need to keep Dobby because he would be crucial in later films)
Holliday felt under pressure during a break in filming over Christmas because people (at a wedding she went to?) kept telling her how much they liked Robin and identified with her character.
Tom didn't notice any pressure until afterwards, mainly because he was really busy with other stuff when he was cast, then went into full on pre production and filming, and then once it was over he thought about it a bit more in a 'hope we didn't mess that up' sort of way. But he is used to doing theatre and playing the same roles as other actor has, so thinks that he is maybe less bothered by the possibility of comparisons with other performances/original books.
There was some discussion about how the filming captured the essence of the London fashion scene, the pressures of celebrity (which JKR is doubtless familiar with), and the fact that Denmark Street was being partly demolished for crossrail while they were filming. The 'Pressures of celebrity' discussion ended up in tongue-in-cheek asides about trashy magazines like Heat which perpetuate the celebrity culture (the chair of the discussion was the Entertainment Editor for Heat)
Q. re physical suitability of casting - i.e. Tom doesn't match description. - Exec Producer had worked with Tom before and had him in mind throughout casting process, plus there's not many 6foot+ actors with pubic hair on their heads. They looked at other actors but Tom kept floating back to the top of Exec Producer's list