Two days in A&E with another one tacked on (5)
I believe the answer is:
added
'one tacked on' is the definition.
(I've seen this in another clue)
'two days in ae with another' is the wordplay.
'two' says to double the letters.
'days' becomes 'd' (abbreviation for days).
'in' means one lot of letters goes inside another.
'with' says to put letters next to each other.
'another' becomes 'd' (I can't justify this - if you can you should give a lot more credence to this answer).
'd' duplicated is 'dd'.
'dd' going inside 'ae' is 'adde'.
'adde'+'d'='ADDED'
Can you help me to learn more?
(Other definitions for added that I've seen before include "Extra" , "Counted up" , "Said" , "Summed up" , "Appended; totalled" .)