The British Chilwell Census lists a contract S/M 6288 of 1 ton 2 wheel GS trailers by Willys. See the attached picture from David Hayward's book on Pearson's of Liverpool. It seems they were used primarily with the F60B 40-mm SP Bofors as stated by Tony above.
The text is not entirely correct: 1-ton trailers were not used with Jeeps, nor was the "F60B converted to SP units and the trailers re-allocated for further use" - the F60B was a SP unit from the onset.
F60B with 1-ton "Ben Hur" trailer, as assembled by Pearson's from Liverpool.
