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