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