Actually between the years 1948 to 1960, Morris offered passenger cars with a 6-cylinder engine.
First was the Morris MS-series Six of 1948, as I understand it was a 6-cylinder version of the MO-series Oxford. Which was replaced by the Isis, effectively once again a 6-cylinder version of the then-current Oxford.
Neither of the two above cars sold well and the Isis was discontinued in 1958. And was the last 6-cylinder Morris built.
According to my "magic" book... The MS-series Six had a 2215cc engine ("ohc engine, fast and has a lovely engine, alas with valve problems"); The Isis had the BMC C-Type engine, 2639cc, ohv
[your history lesson for the day...]