The plane depicted as bringing Uncle Joshua back to London at Heathrow is a 1945 Avro Type 685 "York" C.1, registration G-AGNZ. It flew with the RAF in WWII and then BOAC, and in 1949 was acquired by Eagle Airways. It crashed after takeoff from Berlin in 1952 due to engine failure and was damaged beyond repair. 259 of all variants were built from 1943 to 1949.
Uncle Joshua Howard:
Mildred, in affairs of the heart, you have all the delicacy of a bulldozer.
Ten people are seated at the dinner table. In a later scene of dancing to a band, 14 people can be seen on the dance floor and they don't include Uncle Joshua, the Marquis of Borechester (George) or Richard.
About one-third into the movie, the screen runs credits that introduce the Borechester family: "Borechester Towers. Ancestral seat of the Marquis of Borechester. "A.D. 1100. The Normans started building the walls... "A.D. 1300. The family started hanging their pictures on the walls... "A.D. 1939. The R.A.F. took over and started scribbling on the walls... "A.D. 1947. A Stately home of England -- with the state coming nearer every budget."