Rocket will rebrand Leapingsalmon kiosks at Victoria, Paddington, London Bridge and Canary Wharf, and take over its fifth site in Charing Cross, which has yet to open.
The sale will bring the Rocket estate up to 11 kiosks.
Rocket has also tied up with major London sandwich chain Benjy’s to offer its entire range at four key locations, Victoria Station, Embankment, Old Broad Street and Cannon Street.
Rocket MD Simon Clarke said: “Acquiring these sites is quite a catch. It means the service can be offered to more commuters across the south east.”
Leapingsalmon will continue to trade at www.leapingsalmon. com. MD James Marshall said it was looking at other retail avenues such as tie-ups with non-food retailers.