One-time London lawyer's heading off to become model (8)
I believe the answer is:
exemplar
'model' is the definition.
(I know that model can be written as exemplar)
'one-time london lawyer's heading off' is the wordplay.
'one time london' becomes 'ex' (I can't justify this - if you can you should give a lot more credence to this answer).
'lawyer' becomes 'templar' (I've seen this before).
'heading off' means to remove the first letter.
'templar' with its initial letter taken away is 'emplar'.
'ex'+'emplar'='EXEMPLAR'
'to become' is the link.
Can you help me to learn more?
(Other definitions for exemplar that I've seen before include "Model to be followed" , "Epitome" , "Something serving as an appropriate model" , "A model or instance" , "Typical specimen" .)