Legal right to deceive the National Front (4)
I believe the answer is:
lien
'legal right' is the definition.
(I've seen this before)
'deceive the national front' is the wordplay.
'deceive' becomes 'lie' (to lie is to deceive people).
'front' indicates taking the first letters.
The first letter of 'national' is 'n'.
'lie'+'n'='LIEN'
'to' acts as a link.
(Other definitions for lien that I've seen before include "The right to take property if an obligation is not met" , "Legal right over the Nile" , "Right to another's property, if an obligation is not discharged" , "Sequestration order" , "Legal claim on Nile" .)