Ice cream cups in 24.48 are almost full with ice cream, but in the next second they become half empty.
When Andy is asking the make up lady for her name for the autograph and he doesn't know her name he asks how to spell it and she replies with 'just the normal way' but in the credits to When the Whistle Blows her name is listed as Anne which can obviously be spelled Ann or Anne so she would have at least answered with, 'with an e at the end'
At 21.06 Sir Ian McKellen mistakenly calls Andy Millman "David". He says "Why thank you David. No David he must kiss you on the lips". This is obviously a reference to Ricky Gervais' role as the brilliant David Brent. It is a moment when Gervais is emulating a Brent style cringe, so possibly McKellen, a fan of The Office, slipped up but his acting in the scene was so good, they decided to keep it in.