The Multi-Unit Space Transport And Recovery Device or MUSTARD was a concept explored by the British Aircraft Corporation (BAC) around 1968 for launching payloads weighing as much as 5,000 lb. into orbit.
MUSTARD was a winged three-stage reusable vehicle which used the triamese concept. The three components of the design were three largely identical lifting bodies (each similar to the Northrop HL-10), stacked back-to-belly.
The units would be stacked for launch, and two of them would act as boosters to launch the third into Earth orbit.
The booster units would feed any excess fuel to the unit which was to be the spacecraft.
At 150,000 to 200,000 ft. (45,750 to 60,960 m) the booster units would separate and land like aircraft. The spacecraft would place its payload into orbit and then return in the same manner. (Wikipedia)
Read more: How Britain missed out on Mustard - Nigel Henbest on the shuttle that didn’t get a chance to take off. New Scientist, 22 May 1986, page 60.
(Drawings: Nagy Ernő: Rakétajárművek. Táncsics Könyvkiadó, Budapest, 1968.)