Euston. Network Rail's headquarters are located outside Euston station.
Alternatively, you might be asking which is the nearest tube station to the National Rail in London. In which case, there are loads of railway terminals in London and each one has its own tube station.
The London Transport Museum? The nearest tube station to the London Transport Museum is Covent Garden, on the Piccadilly line. It's so near the announcement says: Alight here for London's Transport Museum.
North Greenwich is the nearest tube station to the O2 arena
Tower Hill - on the circle and district lines
Either North Greenwich or Canning Town. They are quite far away, but an easier link to London City Airport is the Docklands Light Railway, which has it's own London City Airport stop!
The nearest tube (underground) station is Tower Hill.
Tower Hill Station is the nearest underground station to Fenchurch Street main line.
Sloane Square, Victoria or Pimlico.
Tower Hill
The nearest tube station is Canada Water station.
Romford doesn't have a tube station but the mainline station has a frequent service to London Liverpool Street. The nearest tube station is Upminster.
Camden Tube Station
Nearest to what
If you mean the Royal Hospital, Chelsea - which isn't a hospital, it's almshouses for retired army personnel - the nearest main line station is Victoria and the nearest underground station is Sloane Square.
Leicester Square has its own tube station.
Westminster
69
Arsenal
Westminster or Waterloo
The nearest tube station is Waterloo.
Oxford Circus