Clap about engineers turning up fuel (4)
I believe the answer is:
derv
'fuel' is the definition.
(I know that derv is a type of diesel fuel)
'clap about engineers turning up' is the wordplay.
'clap' becomes 'vd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' is an insertion indicator.
'engineers' becomes 're' (Royal Engineers).
'turning up' says the letters should be written in reverse.
'vd' placed around 're' is 'vred'.
'vred' written backwards gives 'DERV'.
Can you help me to learn more?
(Other definitions for derv that I've seen before include "Fuel for lorries" , "Vehicle diesel-oil" , "Lorry fuel" , "Diesel engine fuel oil" , "Type of fuel" .)