His production credits covered a wide variety of styles — he also produced the original cast recordings of musicals such as Hello, Dolly!, Fings Ain't Wot They Used T'Be, Oh!
Through his efforts, David Bowie, John Mayall, Caravan, and Genesis signed with Decca, although the records of some of these artists appeared on the Deram imprint.
He gave the Moody Blues the support that enabled them to evolve from a struggling 'beat-pop' act into a full-fledged progressive rock group, and he offered them a deal to record a lavish orchestral concept album that would promote the company's DSS stereo sound system.
Mendl also backed the group's groundbreaking demand for complete artistic control over the resulting album, Days of Future Passed, recorded with the London Festival Orchestra, and for which he acted as executive producer, as well as writing the liner notes.
When Mendl returned to work, he discovered that his office had been cleaned out on the orders of the new proprietors, and all his diaries — which would have provided a unique insight into the company's operations — had been thrown away.