What was the name of the train that took Queen Elizabeth's father from Sandringham to London after his death?

The train that carried George VI was named Windsor Castle.

George VI died on 6th February 1952 at Sandringham and was buried at St George's Chapel, Windsor Castle, on 15th February 1952, following a State Funeral in the Chapel. His daughter, HRH The Princess Elizabeth, had been proclaimed Queen Elizabeth II on 8th February 1952. George VI's coffin was brought to Windsor by steam train hauled by the engine 'Windsor Castle' seen here at Paddington Station in London

http://www.thamesweb.co.uk/windsor/windsorhistory/royalfunerals/geovi_funeral52.html
This is the Royal Windsor website so I would have thought that they actually knew the correct answer.

Apparently this journey used TWO trains.

The body of the late King George VI was brought from Sandringham to London by rail on Monday, February 11. The special train was made up of nine vehicles, all of which were in the varnished teak livery of the former L.N.E.R., except the hearse-coach, which was painted black with a white roof. It was hauled from Wolferton (the station for Sandringham) to Kings Lynn by the ‘Sandringham' class 4-6-0 locomotive No. 61617, Ford Castle. After reversal at Kings Lynn, the train continued its journey via Cambridge, and Hitchin to Kings Cross behind the first of the new class ‘7' Pacifics, No. 70000 Britannia. The departure time from Wolferton was 12.5 p.m., and Kings Cross was reached punctually at 2.45 p.m. The body of the King was then taken to Westminster Hall to lie in state for three days.

http://www.york.ac.uk/inst/irs/irshome/features/readings/archive/royal.htm

With regards to the journey from London to Windsor, it was not actually the "Windsor Castle" engine although it appeared to be.

A trial run of the funeral train from Paddington to Windsor was made on Tuesday, February 12, behind the Western Region ‘Castle' class locomotive No. 7013, Bristol Castle, in charge of Driver Albert Potter. The train gained time slightly on the 21½-mile journey, and reached Windsor two min. early.

Special trains were run from Paddington to Windsor in advance of the funeral train, and the special for mourners in the procession started from platform No. 9 at 12.20 p.m., hauled by 4-6-0 engine No. 7004, Eastnor Castle. The funeral train left at 12.35 p.m., headed by an engine of the ‘Castle' class bearing the name Windsor Castle , in charge of Driver Potter and Fireman H. T. Bliss, both of Old Oak. Draped plaques of the Royal Coat of Arms were displayed on each side of the smokebox of the locomotive.

HOWEVER !

The engine was not, in fact, No. 4082, Windsor Castle, built in April, 1924, which hauled the funeral train of King George V in January, 1936, but No. 7013, Bristol Castle, built in 1948. No. 4082 had been sent to Swindon for overhaul shortly before the death of the King, and was not available on February 15. It was felt, however, that it would be a fitting tribute to King George VI if the engine of the funeral train bore the same name as that used on the occasion of the funeral of his father, and the nameplates and numberplates of No. 4082 were transferred to No. 7013. The brass plates on the cab of Windsor Castle, which commemorate the occasion in 1924 when King George V drove the engine 3/4 mile to Swindon Station, also were transferred to Bristol Castle. It is understood that the substitution of the nameplates and numberplates will be permanent.