Nitrogen is removed from a liquefied natural gas feed (41 ) by a two stage separation in which the liquefied natural gas (41 ) is first fractionated (23) to provide a first nitrogen-enriched overhead vapour stream (46) and a nitrogen- containing bottoms liquid stream (19) and then at least a portion of said bottoms liquid stream (19) is fractionated (25) to provide a second nitrogen-enriched overhead vapour stream (36) that is of lower purity than said first overhead vapour stream (46) and a purified liquefied natural gas stream (50). The first fractionation is conducted in a distillation column (23) refluxed (45) with nitrogen overhead (43) condensed in a condenser (24) located in a flash drum (25) in which the second fractionation is conducted. The provision of two nitrogen-containing streams (26, 36) of different concentration permits control of the nitrogen content of fuel gas for use in the natural gas liquefaction plant.