Travel company in outskirts of Barnet for Londoners (7)
I believe the answer is:
airline
I believe this is a double definition.
'travel company' is the first definition.
(company working in air travel)
'outskirts of barnet for londoners' is the second definition.
('hairline' - Barnet Fair is Cockney rhyming slang for hair - said with the 'H' dropped - a cockney accent.)
'in' is the link.
(Other definitions for airline that I've seen before include "SAS, say" , "company supplying transport" , "Virgin, possibly" , "Company operating flying machines" , "Transport business" .)