The man in the picture that Oz sticks up on the wall is Arthur Scargill. Scargill was the leader of the National Union of Miners, and led the big British strike in the eighties. He now leads the Socialist Labour Party in the UK. He was seen by many people as being the main opponent of Prime Minister Margaret Thatcher.
When Oz and Moxey are unloading the van after their shopping trip to Asda, they whistle a jingle and tap their back pockets. This is a reference to the popular and long-running "Asda Price" advertising campaign, in which this tune was followed by customers tapping their pockets twice (producing a chinking noise from the extra money they have saved).
In joke: Moxey says "it's not too bad, once you get inside, a bit like prison really" when they reach Thornley Manor at night. The prison scene at the beginning of series 2, when Moxey and another prisoner are plastering a room for Mr Galloway, was filmed in the same building.
Dennis refers to the retirement home rooms as "Little Boxes". This comes from the Pete Seeger song of 1963. The song is a political satire about the development of suburbia and associated conformist middle-class attitudes. It refers to suburban tract housing as "little boxes" of different colors "all made out of ticky-tacky", and which "all look just the same." "Ticky-tacky" is a reference to the shoddy material used in the construction of housing of that time.
The tower on the side of Thornley Manor was built by the production crew, to make the building look more Victorian. It is not part of the original structure.