ΔE 16.8, loose: different enough that you should pick on purpose. Splinter Green is noticeably darker, more muted than Hemp BS4800/10B21.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Splinter Green is noticeably darker, more muted than Hemp BS4800/10B21.
The same difference applies the other way round: Hemp BS4800/10B21 is noticeably lighter, more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Hemp BS4800/10B21 on the colour wheel See Splinter Green on the colour wheel
All matches: Hemp BS4800/10B21 equivalents · Splinter Green equivalents