Here is the full list of all 25 Her Majesty's SPIFFING achievements.
Wake up Sub Lieutenant Jones
Ensure no one can erase the driver
Locate the paperclip
Examine the Gravity Simulation Switch
Talk to G.E.R.T.E.A. about British villains
Look intently at Sub Lieutenant Jones
Crush a table top football player
Commence your mission on board the HMSS Imperialise!
Attempt to mix washing up liquid and tea
Give Sub Lieutenant Jones English's tea
Crash into ejected fuel cell when at the controls of the HMSS Imperialise
Break a sweat when using the treadmill
Use the ladder like a boss
Find the replacement motor
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?
Observe Schrödinger's cat both alive and dead
Put frogs to sleep
Fail to catch a frog even when they are asleep
Save game progress using the typewriter
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