Thatcher's work is ... free (2,3,5)
I believe the answer is:
on the house
'is free' is the definition.
(something on the house is given free of charge)
'thatcher's work' is the wordplay.
I cannot really understand how this works, but
'work' could be 'use' (I've seen this in another clue) and 'use' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for on the house that I've seen before include "Where satellite dish may be" , "With the management's compliments" , "for no money" , "Where roof slates should be going" , "Roof tiles so" .)