Reg Lane development to increase in size (7)
I believe the answer is:
enlarge
'increase in size' is the definition.
(I've seen this before)
'reg lane development' is the wordplay.
'development' indicates anagramming the letters.
'reg'+'lane'='reglane'
'reglane' is an anagram of 'ENLARGE'.
'to' is the link.
(Other definitions for enlarge that I've seen before include "go into greater detail" , "Gleaner (anag.)" , "Widen" , "Wax" , "Make greater" .)