Continuity mistake: Hugo Dore goes over to the bookshelf empty-handed; in the next shot, he picks up a book and now has a cup of coffee in his right hand. In the next shot of him giving Joey Ross the book, the cup has gone again.(00:36:00)
Continuity mistake: Hugo puts his mug down on the table before going to fetch a book. As turns back from the shelf, the mug is back in his hand, and then as he crosses the room, it is gone again.(00:35:55)
Plot hole: Ian Avery-Cooper loses his lottery ticket which is immediately picked up and appropriated by Leonard Corbyn. However, Avery-Cooper immediately reports the loss to the shopkeeper who sold him the ticket. All lottery sales staff are trained in what to do under these circumstances, because it happens a lot - they cancel the lost ticket and issue a new one. Since Avery-Cooper used the same numbers every week this would not pose a problem, but even if he didn't the ticket would be recorded on the seller's computers and could be precisely reconstructed. This would be even easier since Avery-Cooper reports the loss within a minute of it happening and we see that he has the receipt for the sale in his hand. Corbyn's stolen ticket would be worthless and Avery-Cooper would be able to claim his rightful winnings. If nothing else Ian could have simply bought another ticket with the same numbers.
Chosen answer: It was a bottle of turpentine.
Methylated spirit, always coloured purple.