Here is the full list of all 25 Her Majesty's SPIFFING achievements.
Attempt to mix washing up liquid and tea
Place washing liquid inside washing machine before it's activated
Acquire a second block of cheese
Find the replacement motor
Observe Schrödinger's cat both alive and dead
Break a sweat when using the treadmill
Ensure no one can erase the driver
Crash into ejected fuel cell when at the controls of the HMSS Imperialise
Give Sub Lieutenant Jones English's tea
Talk to G.E.R.T.E.A. about British villains
Look intently at Sub Lieutenant Jones
Complete Her Majesty's SPIFFING: The Empire Staggers Back
Fail to catch a frog even when they are asleep
Put frogs to sleep
Save game progress using the typewriter
Examine all the rocks on the planet surface
Maybe it was earth all along?
Summon the Power of Greyskull to distract Antoine and Pierre
Locate the French camp while driving the Beagle Two Too
Use the ladder like a boss
Wake up Sub Lieutenant Jones
Crush a table top football player
Examine the Gravity Simulation Switch
Locate the paperclip
Commence your mission on board the HMSS Imperialise!