The ending of "To Hull and Back"
I saw this last night, and it was one of the best episodes of OFAH I've seen.
However, I have to wonder if that £15,000 of banknotes that Derek threw off of the Trotter's balcony was counterfeit or real? Rodney blabbers about the signs it was genuine banknotes, and even Uncle Albert is shocked and disbelieving as well, but Derek is confident they were counterfeit, like the other money they used earlier in the story.
Wikipedia says it was real, and I'd say that as well. In other words, Derek just proved to himself how stupid he was by literally throwing away a mini-fortune. The money they got from the two genuine diamonds eventually being all they had!