Blow up in middle of Hertfordshire, in brief (5)
I believe the answer is:
erupt
'blow' is the definition.
(I've seen this in another clue)
'up in middle of hertfordshire in brief' is the wordplay.
'in' means one lot of letters goes inside another.
'middle of' indicates the central letters.
'in' means one lot of letters goes inside another.
'brief' becomes 'et' (I can't explain this - if you can you should believe this answer much more).
The central letter of 'hertfordshire' is 'r'.
'r' put within 'et' is 'ert'.
'up' placed within 'ert' is 'ERUPT'.
Can you help me to learn more?
(Other definitions for erupt that I've seen before include "spout" , "Spurt lava" , "Emit lava" , "Explode" , "Suddenly appear" .)